A lot of you probably know Project Euler.

For those who don't here a short explanation: Project Euler is a collection of mathematical/programming problems.
Most problems consist of finding a single number and are solved by writing a program in the programming language of your choice.

Most people solve these by using normal languages like C, Java, Phyton, Haskell etc.
But you can also go a step further and try solving it with a little bit more exotic languages.

So here are my solutions written in Befunge

**Note:**

Similar to most Befunge content on this site I only used the Befunge-93 instruction-set but ignored the 80x25 size restriction.

Still I tries to keep the programs in the Befunge-93 grid size, but that wasn't possible for all. So I guess some programs are *technically* Befunge-98.

Also the original befunge-93 spec didn't specify the word size of the stack or the grid

So, while most programs run happily with 32bit integers some need an interpreter that supports 64bit integers for both stack and grid.

I have a included javascript runner here, but for one I only enabled it for programs of reasonable sizes (a few soutions had source files in the megabyte range).

And also it's not the fastest interpreter and some solution take quite a while to finish.

I recommend using BefunExec. I specially made that interpreter for this project. It can run befunge code with around 6.5 MHz *(on my machine)*

# My favorites:

# All solved problems

Number | Title | Time | Size | Solution (hover to reveal) |

1 |
Multiples of 3 and 5 |
62ms |
30x5 Bef-93 |
233,168 |

2 |
Even Fibonacci numbers |
62ms |
26x5 Bef-93 |
4,613,732 |

3 |
Largest prime factor |
9.55s |
55x4 Bef-93 |
6,857 |

4 |
Largest palindrome product |
1min 17s |
71x6 Bef-93 |
906,609 |

5 |
Smallest multiple |
47ms |
73x6 Bef-93 |
232,792,560 |

6 |
Sum square difference |
7.35s |
72x16 Bef-93 |
25,164,150 |

7 |
10001st prime |
7.63s |
1000x156 Bef-98 |
104,743 |

8 |
Largest product in a series |
234ms |
116x29 Bef-98 |
23,514,624,000 |

9 |
Special Pythagorean triplet |
6min 34s |
79x7 Bef-93 |
31,875,000 |

10 |
Summation of primes |
1min 7s |
2000x1007 Bef-98 |
142,913,828,922 |

11 |
Largest product in a grid |
78ms |
151x31 Bef-98 |
70,600,674 |

12 |
Highly divisible triangular number |
7.57s |
1000x170 Bef-98 |
76,576,500 |

13 |
Large sum |
78ms |
59x113 Bef-98 |
5,537,376,230 |

14 |
Longest Collatz sequence |
11min |
51x5 Bef-93 |
837,799 |

15 |
Lattice paths |
47ms |
78x27 Bef-98 |
137,846,528,820 |

16 |
Power digit sum |
4.23s |
60x14 Bef-93 |
1,366 |

17 |
Number letter counts |
47ms |
48x15 Bef-93 |
21,124 |

18 |
Maximum path sum I |
16ms |
120x16 Bef-98 |
1,074 |

19 |
Counting Sundays |
546ms |
72x12 Bef-93 |
171 |

20 |
Factorial digit sum |
265ms |
101x6 Bef-98 |
648 |

21 |
Amicable numbers |
1min 42s |
400x33 Bef-98 |
31,626 |

22 |
Names scores |
16min |
109x5164 Bef-98 |
871,198,282 |

23 |
Non-abundant sums |
32min |
400x88 Bef-98 |
4,179,871 |

24 |
Lexicographic permutations |
31ms |
61x8 Bef-93 |
2,783,915,460 |

25 |
1000-digit Fibonacci number |
1min 56s |
123x28 Bef-98 |
4,782 |

26 |
Reciprocal cycles |
4.48s |
100x16 Bef-98 |
983 |

27 |
Quadratic primes |
6.24s |
600x162 Bef-98 |
-59,231 |

28 |
Number spiral diagonals |
15ms |
54x2 Bef-93 |
669,171,001 |

29 |
Distinct powers |
23min |
248x59 Bef-98 |
9,183 |

30 |
Digit fifth powers |
7.33s |
59x8 Bef-93 |
443,839 |

31 |
Coin sums |
47s |
60x11 Bef-93 |
73,682 |

32 |
Pandigital products |
7.19s |
166x21 Bef-98 |
45,228 |

33 |
Digit canceling fractions |
109ms |
67x18 Bef-93 |
100 |

34 |
Digit factorials |
1min 20s |
45x7 Bef-93 |
40,730 |

35 |
Circular primes |
27s |
2000x516 Bef-98 |
55 |

36 |
Double-base palindromes |
172ms |
78x8 Bef-93 |
872,187 |

37 |
Truncatable primes |
20s |
2000x514 Bef-98 |
748,317 |

38 |
Pandigital multiples |
624ms |
169x6 Bef-98 |
932,718,654 |

39 |
Integer right triangles |
827ms |
72x6 Bef-93 |
840 |

40 |
Champernowne's constant |
16ms |
69x7 Bef-93 |
210 |

41 |
Pandigital prime |
31ms |
40x17 Bef-93 |
7,652,413 |

42 |
Coded triangle numbers |
406ms |
112x1788 Bef-98 |
162 |

43 |
Sub-string divisibility |
140ms |
68x23 Bef-93 |
16,695,334,890 |

44 |
Pentagon numbers |
4min 18s |
60x11 Bef-93 |
5,482,660 |

45 |
Triangular, pentagonal, and hexagonal |
3.49s |
48x6 Bef-93 |
1,533,776,805 |

46 |
Goldbach's other conjecture |
13s |
200x57 Bef-98 |
5,777 |

47 |
Distinct primes factors |
8min 57s |
400x518 Bef-98 |
134,043 |

48 |
Self powers |
3.73s |
37x3 Bef-93 |
9,110,846,700 |

49 |
Prime permutations |
124ms |
66x8 Bef-93 |
296,962,999,629 |

50 |
Consecutive prime sum |
30s |
2000x512 Bef-98 |
997,651 |

51 |
Prime digit replacements |
1min 53s |
78x20 Bef-93 |
121,313 |

52 |
Permuted multiples |
2.92s |
45x6 Bef-93 |
142,857 |

53 |
Combinatoric selections |
125ms |
80x7 Bef-93 |
4,075 |

54 |
Poker hands |
2.54s |
118x1009 Bef-98 |
376 |

55 |
Lychrel numbers |
2.22s |
56x5 Bef-93 |
249 |

56 |
Powerful digit sum |
13s |
75x11 Bef-93 |
972 |

57 |
Square root convergents |
15s |
80x54 Bef-98 |
153 |

58 |
Spiral primes |
12s |
50x17 Bef-93 |
26,241 |

59 |
XOR decryption |
6.30s |
273x128 Bef-98 |
107,359 |

60 |
Prime pair sets |
33min |
3323x3360 Bef-98 |
26,033 |

61 |
Cyclical figurate numbers |
14s |
80x25 Bef-93 |
28,684 |

62 |
Cubic permutations |
6min 3s |
505x58 Bef-98 |
127,035,954,683 |

63 |
Powerful digit counts |
2.76s |
80x10 Bef-93 |
49 |

64 |
Odd period square roots |
5.80s |
51x9 Bef-93 |
1,322 |

65 |
Convergents of e |
124ms |
80x14 Bef-93 |
272 |

66 |
Diophantine equation |
55s |
80x25 Bef-93 |
661 |

67 |
Maximum path sum II |
266ms |
299x101 Bef-98 |
7,273 |

68 |
Magic 5-gon ring |
78ms |
39x25 Bef-93 |
6,531,031,914,842,725 |

69 |
Totient maximum |
16ms |
80x10 Bef-93 |
510,510 |

70 |
Totient permutation |
3.71s |
150x47 Bef-98 |
8,319,823 |

71 |
Ordered fractions |
11s |
73x8 Bef-93 |
428,570 |

72 |
Counting fractions |
50s |
486x1047 Bef-98 |
303,963,552,391 |

73 |
Counting fractions in a range |
3min 22s |
2000x12010 Bef-98 |
7,295,372 |

74 |
Digit factorial chains |
49s |
1224x833 Bef-98 |
402 |

75 |
Singular integer right triangles |
39s |
1000x1515 Bef-98 |
161,667 |

76 |
Counting summations |
32ms |
104x108 Bef-98 |
190,569,291 |

77 |
Prime summations |
47ms |
101x39 Bef-98 |
71 |

78 |
Coin partitions |
2min 50s |
251x256 Bef-98 |
55,374 |

79 |
Passcode derivation |
0ms |
56x21 Bef-93 |
73,162,890 |

80 |
Square root digital expansion |
1min 56s |
69x18 Bef-93 |
40,886 |

81 |
Path sum: two ways |
234ms |
500x180 Bef-98 |
427,337 |

82 |
Path sum: three ways |
2.11s |
500x180 Bef-98 |
260,324 |

83 |
Path sum: four ways |
1.75s |
500x180 Bef-98 |
425,185 |

84 |
Monopoly odds |
19s |
77x20 Bef-93 |
101,524 |

85 |
Counting rectangles |
109ms |
35x8 Bef-93 |
2,772 |

86 |
Cuboid route |
1min 31s |
66x10 Bef-93 |
1,818 |

87 |
Prime power triples |
27s |
1000x1018 Bef-98 |
1,097,343 |

88 |
Product-sum numbers |
23s |
1024x50 Bef-98 |
7,587,457 |

89 |
Roman numerals |
78ms |
73x1009 Bef-98 |
743 |

90 |
Cube digit pairs |
54s |
80x45 Bef-98 |
1,217 |

91 |
Right triangles with integer coordinates |
343ms |
36x5 Bef-93 |
14,234 |

92 |
Square digit chains |
6min 19s |
80x16 Bef-93 |
8,581,146 |

93 |
Arithmetic expressions |
42s |
111x211 Bef-98 |
1,258 |

94 |
Almost equilateral triangles |
0ms |
40x5 Bef-93 |
518,408,346 |

95 |
Amicable chains |
4min 2s |
2017x1035 Bef-98 |
14,316 |

96 |
Su Doku |
1min 30s |
218x50 Bef-98 |
24,702 |

97 |
Large non-Mersenne prime |
21s |
13x5 Bef-93 |
8,739,992,577 |

98 |
Anagramic squares |
22s |
258x199 Bef-98 |
18,769 |

99 |
Largest exponential |
1.11s |
63x1000 Bef-98 |
709 |

100 |
Arranged probability |
0ms |
56x3 Bef-93 |
756,872,327,473 |

101 |
Optimum polynomial |
250ms |
83x37 Bef-98 |
37,076,114,526 |

102 |
Triangle containment |
281ms |
80x1009 Bef-98 |
228 |