Referenser:
- https://code.google.com/p/projecteuler-solutions/wiki/ProjectEulerSolutions
- http://eulersolutions.fr.yuku.com
- http://nayuki.eigenstate.org/page/project-euler-solutions

Fuska inte med lösningar!

Problem 1: Multiples of 3 and 5
   233168

Problem 2: Even Fibonacci numbers
   4613732

Problem 3: Largest prime factor
   6857

Problem 4: Largest palindrome product
   906609

Problem 5: Smallest multiple
   232792560

Problem 6: Sum square difference
   25164150

Problem 7: 10001st prime
   104743

Problem 8: Largest product in a series
   40824

Problem 9: Special Pythagorean triplet
   31875000

Problem 10: Summation of primes
   142913828922

Problem 11: Largest product in a grid
   70600674

Problem 12: Highly divisible triangular number
   76576500

Problem 13: Large sum
   5537376230

Problem 14: Longest Collatz sequence
   837799

Problem 15: Lattice paths
   137846528820

Problem 16: Power digit sum
   1366

Problem 17: Number letter counts
   21124

Problem 18: Maximum path sum I
   1074

Problem 19: Counting Sundays
   171

Problem 20: Factorial digit sum
   648

Problem 21: Amicable numbers
   31626

Problem 22: Names scores
   871198282

Problem 23: Non-abundant sums
   4179871

Problem 24: Lexicographic permutations
   2783915460

Problem 25: 1000-digit Fibonacci number
   4782

Problem 26: Reciprocal cycles
   983

Problem 27: Quadratic primes
   -59231

Problem 28: Number spiral diagonals
   669171001

Problem 29: Distinct powers
   9183

Problem 30: Digit fifth powers
   443839

Problem 31: Coin sums
   73682

Problem 32: Pandigital products
   45228

Problem 33: Digit canceling fractions
   100

Problem 34: Digit factorials
   40730

Problem 35: Circular primes
   55

Problem 36: Double-base palindromes
   872187

Problem 37: Truncatable primes
   748317

Problem 38: Pandigital multiples
   932718654

Problem 39: Integer right triangles
   840

Problem 40: Champernowne's constant
   210

Problem 41: Pandigital prime
   7652413

Problem 42: Coded triangle numbers
   162

Problem 43: Sub-string divisibility
   16695334890

Problem 44: Pentagon numbers
   5482660

Problem 45: Triangular, pentagonal, and hexagonal
   1533776805

Problem 46: Goldbach's other conjecture
   5777

Problem 47: Distinct primes factors
   134043

Problem 48: Self powers
   9110846700

Problem 49: Prime permutations
   296962999629

Problem 50: Consecutive prime sum
   997651

Problem 51: Prime digit replacements
   121313

Problem 52: Permuted multiples
   142857

Problem 53: Combinatoric selections
   4075

Problem 54: Poker hands
   376

Problem 55: Lychrel numbers
   249

Problem 56: Powerful digit sum
   972

Problem 57: Square root convergents
   153

Problem 58: Spiral primes
   26241

Problem 59: XOR decryption
   107359

Problem 60: Prime pair sets
   26033

Problem 61: Cyclical figurate numbers
   28684

Problem 62: Cubic permutations
   127035954683

Problem 63: Powerful digit counts
   49

Problem 64: Odd period square roots
   1322

Problem 65: Convergents of e
   272

Problem 66: Diophantine equation
   661

Problem 67: Maximum path sum II
   7273

Problem 68: Magic 5-gon ring
   6531031914842725

Problem 69: Totient maximum
   510510

Problem 70: Totient permutation
   8319823

Problem 71: Ordered fractions
   428570

Problem 72: Counting fractions
   303963552391

Problem 73: Counting fractions in a range
   7295372

Problem 74: Digit factorial chains
   402

Problem 75: Singular integer right triangles
   161667

Problem 76: Counting summations
   190569291

Problem 77: Prime summations
   71

Problem 78: Coin partitions
   55374

Problem 79: Passcode derivation
   73162890

Problem 80: Square root digital expansion
   40886

Problem 81: Path sum: two ways
   427337

Problem 82: Path sum: three ways
   260324

Problem 83: Path sum: four ways
   425185

Problem 84: Monopoly odds
   101524

Problem 85: Counting rectangles
   2772

Problem 86: Cuboid route
   1818

Problem 87: Prime power triples
   1097343

Problem 88: Product-sum numbers
   7587457

Problem 89: Roman numerals
   743

Problem 90: Cube digit pairs
   1217

Problem 91: Right triangles with integer coordinates
   14234

Problem 92: Square digit chains
   8581146

Problem 93: Arithmetic expressions
   1258

Problem 94: Almost equilateral triangles
   518408346

Problem 95: Amicable chains
   14316

Problem 96: Su Doku
   24702

Problem 97: Large non-Mersenne prime
   8739992577

Problem 98: Anagramic squares
   18769

Problem 99: Largest exponential
   709

Problem 100: Arranged probability
   756872327473

Problem 101: Optimum polynomial
   37076114526

Problem 102: Triangle containment
   228

Problem 103: Special subset sums: optimum
   20313839404245

Problem 104: Pandigital Fibonacci ends
   329468

Problem 105: Special subset sums: testing
   73702

Problem 106: Special subset sums: meta-testing
   21384

Problem 107: Minimal network
   259679

Problem 108: Diophantine reciprocals I
   180180

Problem 109: Darts
   38182

Problem 110: Diophantine reciprocals II
   9350130049860600

Problem 111: Primes with runs
   612407567715

Problem 112: Bouncy numbers
   1587000

Problem 113: Non-bouncy numbers
   51161058134250

Problem 114: Counting block combinations I
   16475640049

Problem 115: Counting block combinations II
   168

Problem 116: Red, green or blue tiles
   20492570929

Problem 117: Red, green, and blue tiles
   100808458960497

Problem 118: Pandigital prime sets
   44680

Problem 119: Digit power sum
   248155780267521

Problem 120: Square remainders
   333082500

Problem 121: Disc game prize fund
   2269

Problem 122: Efficient exponentiation
   1582

Problem 123: Prime square remainders
   21035

Problem 124: Ordered radicals
   21417

Problem 125: Palindromic sums
   2906969179

Problem 126: Cuboid layers
   18522

Problem 127: abc-hits
   18407904

Problem 128: Hexagonal tile differences
   14516824220

Problem 129: Repunit divisibility
   1000023

Problem 130: Composites with prime repunit property
   149253

Problem 131: Prime cube partnership
   173

Problem 132: Large repunit factors
   843296

Problem 133: Repunit nonfactors
   453647705

Problem 134: Prime pair connection
   18613426663617118

Problem 135: Same differences
   4989

Problem 136: Singleton difference
   2544559

Problem 137: Fibonacci golden nuggets
   1120149658760

Problem 138: Special isosceles triangles
   1118049290473932

Problem 139: Pythagorean tiles
   10057761

Problem 140: Modified Fibonacci golden nuggets
   5673835352990

Problem 141: Investigating progressive numbers,
   878454337159

Problem 142: Perfect Square Collection
   1006193

Problem 143: Investigating the Torricelli point of a triangle
   30758397

Problem 144: Investigating multiple reflections of a laser beam.
   354

Problem 145: How many reversible numbers are there below one-billion?
   608720

Problem 146: Investigating a Prime Pattern
   676333270

Problem 147: Rectangles in cross-hatched grids
   846910284

Problem 148: Exploring Pascal's triangle.
   2129970655314432

Problem 149: Searching for a maximum-sum subsequence.
   52852124

Problem 150: Searching a triangular array for a sub-triangle having minimum-sum.
   -271248680

Problem 151: Paper sheets of standard sizes: an expected-value problem.
   0.464399

Problem 152: Writing 1/2 as a sum of inverse squares
   301

Problem 153: Investigating Gaussian Integers
   17971254122360635

Problem 154: Exploring Pascal's pyramid.
   479742450

Problem 155: Counting Capacitor Circuits.
   3857447

Problem 156: Counting Digits
   21295121502550

Problem 157: Solving the diophantine equation
   53490

Problem 158: Exploring strings for which only one character comes lexicographically after its neighbour to the left.
   409511334375

Problem 159: Digital root sums of factorisations.

   14489159

Problem 160: Factorial trailing digits
   16576

Problem 161: Triominoes
   20574308184277971

Problem 162: Hexadecimal numbers
   3D58725572C62302

Problem 163: Cross-hatched triangles
   343047

Problem 164: Numbers for which no three consecutive digits have a sum greater than a given value.
   378158756814587

Problem 165: Intersections
   2868868

Problem 166: Criss Cross
   7130034

Problem 167: Investigating Ulam sequences
   3916160068885

Problem 168: Number Rotations
   59206

Problem 169: Exploring the number of different ways a number can be expressed as a sum of powers of 2.

   178653872807

Problem 170: Find the largest 0 to 9 pandigital that can be formed by concatenating products.
   9857164023

Problem 171: Finding numbers for which the sum of the squares of the digits is a square.
   142989277

Problem 172: Investigating numbers with few repeated digits.
   227485267000992000

Problem 173: Using up to one million tiles how many different "hollow" square laminae can be formed?
   1572729

Problem 174: Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements.
   209566

Problem 175: Fractions involving the number of different ways a number can be expressed as a sum of powers of 2.
   1,13717420,8

Problem 176: Right-angled triangles that share a cathetus.
   96818198400000

Problem 177: Integer angled Quadrilaterals.
   129325

Problem 178: Step Numbers
   126461847755

Problem 179: Consecutive positive divisors

   986262

Problem 180: Rational zeros of a function of three variables.
   285196020571078987

Problem 181: Investigating in how many ways objects of two different colours can be grouped.
   83735848679360680

Problem 182: RSA encryption
   399788195976

Problem 183: Maximum product of parts
   48861552

Problem 184: Triangles containing the origin.
   1725323624056

Problem 185: Number Mind
   4640261571849533

Problem 186: Connectedness of a network.
   2325629

Problem 187: Semiprimes
   17427258

Problem 188: The hyperexponentiation of a number
   95962097

Problem 189: Tri-colouring a triangular grid
   10834893628237824

Problem 190: Maximising a weighted product

   371048281

Problem 191: Prize Strings
   1918080160

Problem 192: Best Approximations
   57060635927998347

Problem 193: Squarefree Numbers
   684465067343069

Problem 194: Coloured Configurations
   61190912

Problem 195: Inscribed circles of triangles with one angle of 60 degrees
   75085391

Problem 196: Prime triplets
   322303240771079935

Problem 197: Investigating the behaviour of a recursively defined sequence
   1.710637717

Problem 198: Ambiguous Numbers
   52374425

Problem 199: Iterative Circle Packing
   0.00396087

Problem 200: Find the 200th prime-proof sqube containing the contiguous sub-string "200"
   229161792008

Problem 201: Subsets with a unique sum
   115039000

Problem 202: Laserbeam
   1209002624

Problem 203: Squarefree Binomial Coefficients
   34029210557338

Problem 204: Generalised Hamming Numbers
   2944730

Problem 205: Dice Game
   0.5731441

Problem 206: Concealed Square
   1389019170

Problem 207: Integer partition equations
   44043947822

Problem 208: Robot Walks
   331951449665644800

Problem 209: Circular Logic
   15964587728784

Problem 210: Obtuse Angled Triangles
   1598174770174689458

Problem 211: Divisor Square Sum
   1922364685

Problem 212: Combined Volume of Cuboids
   328968937309

Problem 213: Flea Circus
   330.721154

Problem 214: Totient Chains
   1677366278943

Problem 215: Crack-free Walls
   806844323190414

Problem 216: Investigating the primality of numbers of the form 2
   5437849

Problem 217: Balanced Numbers
   6273134

Problem 218: Perfect right-angled triangles
   0

Problem 219: Skew-cost coding
   64564225042

Problem 220: Heighway Dragon
   139776,963904

Problem 221: Alexandrian Integers
   1884161251122450

Problem 222: Sphere Packing
   1590933

Problem 223: Almost right-angled triangles I
   61614848

Problem 224: Almost right-angled triangles II
   4137330

Problem 225: Tribonacci non-divisors
   2009

Problem 226: A Scoop of Blancmange
   0.11316017

Problem 227: The Chase
   3780.618622

Problem 228: Minkowski Sums
   86226

Problem 229: Four Representations using Squares
   11325263

Problem 230: Fibonacci Words
   850481152593119296

Problem 231: The prime factorisation of binomial coefficients
   7526965179680

Problem 232: The Race
   0.83648556

Problem 233: Lattice points on a circle
   271204031455541309

Problem 234: Semidivisible numbers
   1259187438574927161

Problem 235: An Arithmetic Geometric sequence
   1.002322108633

Problem 236: Luxury Hampers
   123/59

Problem 237: Tours on a 4 x n playing board
   15836928

Problem 238: Infinite string tour
   9922545104535661

Problem 239: Twenty-two Foolish Primes
   0.001887854841

Problem 240: Top Dice
   7448717393364181966

Problem 241: Perfection Quotients
   482316491800641154

Problem 242: Odd Triplets
   997104142249036713

Problem 243: Resilience
   892371480

Problem 244: Sliders
   96356848

Problem 245: Coresilience
   288084712410001

Problem 246: Tangents to an ellipse
   810834388

Problem 247: Squares under a hyperbola
   782252

Problem 248: Numbers for which Euler’s totient function equals 13!
   23507044290

Problem 249: Prime Subset Sums
   9275262564250418

Problem 250: 250250
   1425480602091519

Problem 251: Cardano Triplets
   18946051

Problem 252: Convex Holes
   104924.0

Problem 253: Tidying up
   11.492847

Problem 254: Sums of Digit Factorials
   8184523820510

Problem 255: Rounded Square Roots
   4.4474011180

Problem 256: Tatami-Free Rooms
   85765680

Problem 257: Angular Bisectors
   139012411

Problem 258: A lagged Fibonacci sequence
   12747994

Problem 259: Reachable Numbers
   20101196798

Problem 260: Stone Game
   167542057

Problem 261: Pivotal Square Sums
   238890850232021

Problem 262: Mountain Range.
   2531.205

Problem 263: An engineers' dream come true
   2039506520

Problem 264: Triangle Centres
   2816417.1055

Problem 265: Binary Circles
   209110240768

Problem 266: Pseudo Square Root
   1096883702440585

Problem 267: Billionaire
   0.999992836187

Problem 268: Counting numbers with at least four distinct prime factors less than 100
   785478606870985

Problem 269: Polynomials with at least one integer root
   1311109198529286

Problem 270: Cutting Squares
   82282080

Problem 271: Modular Cubes, part 1
   4617456485273129588

Problem 272: Modular Cubes, part 2
   8495585919506151122

Problem 273: Sum of Squares
   2032447591196869022

Problem 274: Divisibility Multipliers
   1601912348822

Problem 275: Balanced Sculptures
   15030564

Problem 276: Primitive Triangles
   5777137137739632912

Problem 277: A Modified Collatz sequence
   1125977393124310

Problem 278: Linear Combinations of Semiprimes
   1228215747273908452

Problem 279: Triangles with integral sides and an integral angle
   416577688

Problem 280: Ant and seeds
   430.088247

Problem 281: Pizza Toppings
   1485776387445623

Problem 282: The Ackermann function
   1098988351

Problem 283: Integer sided triangles for which the  area/perimeter ratio is integral.
   28038042525570324

Problem 284: Steady Squares
   5a411d7b

Problem 285: Pythagorean odds
   157055.80999

Problem 286: Scoring probabilities
   52.6494571953

Problem 287: Quadtree encoding (a simple compression algorithm)
   313135496

Problem 288: An enormous factorial
   605857431263981935

Problem 289: Eulerian Cycles
   6567944538

Problem 290: Digital Signature
   20444710234716473

Problem 291: Panaitopol Primes
   4037526

Problem 292: Pythagorean Polygons
   3600060866

Problem 293: Pseudo-Fortunate Numbers
   2209

Problem 294: Sum of digits - experience #23
   789184709

Problem 295: Lenticular holes
   4884650818

Problem 296: Angular Bisector and Tangent
   1137208419

Problem 297: Zeckendorf Representation
   2252639041804718029

Problem 298: Selective Amnesia
   1.76882294

Problem 299: Three similar triangles
   549936643

Problem 300: Protein folding
   8.0540771484375

Problem 301: Nim
   2178309

Problem 302: Strong Achilles Numbers
   1170060

Problem 303: Multiples with small digits
   1111981904675169

Problem 304: Primonacci
   283988410192

Problem 305: Reflexive Position
   18174995535140

Problem 306: Paper-strip Game
   852938

Problem 307: Chip Defects
   0.7311720251

Problem 308: An amazing Prime-generating Automaton
   1539669807660924

Problem 309: Integer Ladders
   210139

Problem 310: Nim Square
   2586528661783

Problem 311: Biclinic Integral Quadrilaterals
   2466018557

Problem 312: Cyclic paths on Sierpiński graphs

   324681947

Problem 313: Sliding game
   2057774861813004

Problem 314: The Mouse on the Moon
   132.52756426

Problem 315: Digital root clocks
   13625242

Problem 316: Numbers in decimal expansions
   542934735751917735

Problem 317: Firecracker
   1856532.8455

Problem 318: 2011 nines
   709313889

Problem 319: Bounded Sequences
   268457129

Problem 320: Factorials divisible by a huge integer
   278157919195482643

Problem 321: Swapping Counters
   2470433131948040

Problem 322: Binomial coefficients divisible by 10
   999998760323313995

Problem 323: Bitwise-OR operations on random integers
   6.3551758451

Problem 324: Building a tower
   96972774

Problem 325: Stone Game II
   54672965

Problem 326: Modulo Summations
   1966666166408794329

Problem 327: Rooms of Doom
   34315549139516

Problem 328: Lowest-cost Search
   260511850222

Problem 329: Prime Frog
   199740353/29386561536000

Problem 330: Euler's Number
   15955822

Problem 331: Cross flips
   467178235146843549

Problem 332: Spherical triangles
   2717.751525

Problem 333: Special partitions
   3053105

Problem 334: Spilling the beans
   150320021261690835

Problem 335: Gathering the beans
   5032316

Problem 336: Maximix Arrangements
   CAGBIHEFJDK

Problem 337: Totient Stairstep Sequences
   85068035

Problem 338: Cutting Rectangular Grid Paper
   15614292

Problem 339: Peredur fab Efrawg
   19823.542204

Problem 340: Crazy Function
   291504964

Problem 341: Golomb's self-describing sequence
   56098610614277014

Problem 342: The totient of a square is a cube
   5943040885644

Problem 343: Fractional Sequences
   269533451410884183

Problem 344: Silver dollar game
   65579304332

Problem 345: Matrix Sum
   13938

Problem 346: Strong Repunits
   336108797689259276

Problem 347: Largest integer divisible by two primes
   11109800204052

Problem 348: Sum of a square and a cube
   1004195061

Problem 349: Langton's ant
   115384615384614952

Problem 350: Constraining the least greatest and the greatest least
   84664213

Problem 351: Hexagonal orchards
   11762187201804552

Problem 352: Blood tests
   378563.260589

Problem 353: Risky moon
   1.2759860331

Problem 354: Distances in a bee's honeycomb
   58065134

Problem 355: Maximal coprime subset
   1726545007

Problem 356: Largest roots of cubic polynomials
   28010159

Problem 357: Prime generating integers
   1739023853137

Problem 358: Cyclic numbers
   3284144505

Problem 359: Hilbert's New Hotel
   40632119

Problem 360: Scary Sphere
   878825614395267072

Problem 361: Subsequence of Thue-Morse sequence
   178476944

Problem 362: Squarefree factors
   457895958010

Problem 363: Bézier Curves
   0.0000372091

Problem 364: Comfortable distance
   44855254

Problem 365: A huge binomial coefficient
   162619462356610313

Problem 366: Stone Game III
   88351299

Problem 367: bozo sort
   48271207

Problem 368: A Kempner-like series
   253.6135092068

Problem 369: Badugi

   862400558448

Problem 370: Geometric triangles

   41791929448408

Problem 371: Licence plates
   40.66368097

Problem 372: Pencils of rays
   301450082318807027

Problem 373: Circumscribed Circles
   727227472448913

Problem 374: Maximum Integer Partition Product

   334420941

Problem 375: Minimum of subsequences
   7435327983715286168

Problem 376: Nontransitive sets of dice
   973059630185670

Problem 377: Sum of digits, experience 13
   732385277

Problem 378: Triangle Triples
   147534623725724718

Problem 379: Least common multiple count
   132314136838185

Problem 380: Amazing Mazes!
   6.3202e25093

Problem 381: (prime-k) factorial
   139602943319822

Problem 382: Generating polygons
   697003956

Problem 383: Divisibility comparison between factorials
   22173624649806

Problem 384: Rudin-Shapiro sequence
   3354706415856332783

Problem 385: Ellipses inside triangles
   3776957309612153700

Problem 386: Maximum length of an antichain
   528755790

Problem 387: Harshad Numbers
   696067597313468

Problem 388: Distinct Lines
   831907372805129931

Problem 389: Platonic Dice
   2406376.3623

Problem 390: Triangles with non rational sides and integral area
   2919133642971

Problem 391: Hopping Game
   61029882288

Problem 392: Enmeshed unit circle
   3.1486734435

Problem 393: Migrating ants
   112398351350823112

Problem 394: Eating pie
   3.2370342194

Problem 395: Pythagorean tree
   28.2453753155

Problem 396: Weak Goodstein sequence
   173214653

Problem 397: Triangle on parabola
   141630459461893728

Problem 398: Cutting rope
   2010.59096

Problem 399: Squarefree Fibonacci Numbers
   1508395636674243,6.5e27330467

Problem 400: Fibonacci tree game
   438505383468410633

Problem 401: Sum of squares of divisors
   281632621

Problem 402: Integer-valued polynomials
   356019862

Problem 403: Lattice points enclosed by parabola and line
   18224771

Problem 404: Crisscross Ellipses
   1199215615081353

Problem 405: A rectangular tiling
   237696125

Problem 406: Guessing Game
   36813.12757207

Problem 407: Idempotents
   39782849136421

Problem 408: Admissible paths through a grid
   299742733

Problem 409: Nim Extreme
   253223948

Problem 410: Circle and tangent line
   799999783589946560

Problem 411: Uphill paths
   9936352

Problem 412: Gnomon numbering
   38788800

Problem 413: One-child Numbers
   3079418648040719

Problem 414: Kaprekar constant
   552506775824935461

Problem 415: Titanic sets
   55859742

Problem 416: A frog's trip
   898082747

Problem 417: Reciprocal cycles II
   446572970925740

Problem 418: Factorisation triples
   1177163565297340320

Problem 419: Look and say sequence
   998567458,1046245404,43363922

Problem 420: 2x2 positive integer matrix
   145159332

Problem 421: Prime factors of
   n/a

Problem 422: Sequence of points on a hyperbola
   n/a

Problem 423: Consecutive die throws
   n/a

Problem 424: Kakuro
   1059760019628

Problem 425: Prime connection
   46479497324

Problem 426: Box-ball system
   n/a

Problem 427: n-sequences
   n/a

Problem 428: Necklace of circles
   n/a

Problem 429: Sum of squares of unitary divisors
   98792821

Problem 430: Range flips
   5000624921.38

Problem 431: Square Space Silo
   n/a

Problem 432: Totient sum
   n/a

Problem 433: Steps in Euclid's algorithm
   326624372659664

Problem 434: Rigid graphs
   863253606

Problem 435: Polynomials of Fibonacci numbers
   252541322550

Problem 436: Unfair wager
   0.5276662759

Problem 437: Fibonacci primitive roots
   74204709657207

Problem 438: Integer part of polynomial equation's solutions
   n/a