1 ! Copyright (c) 2008 Aaron Schaefer.
2 ! See https://factorcode.org/license.txt for BSD license.
3 USING: kernel math.combinatorics math.primes sequences
7 ! https://projecteuler.net/problem=41
12 ! We shall say that an n-digit number is pandigital if it makes
13 ! use of all the digits 1 to n exactly once. For example, 2143
14 ! is a 4-digit pandigital and is also prime.
16 ! What is the largest n-digit pandigital prime that exists?
22 ! Check 7-digit pandigitals because if the sum of the digits in
23 ! any number add up to a multiple of three, then it is a
24 ! multiple of three and can't be prime. I assumed there would be
25 ! a 7-digit answer, but technically a higher 4-digit pandigital
26 ! than the one given in the description was also possible.
28 ! 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45
29 ! 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36
30 ! 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28 *** not divisible by 3 ***
31 ! 1 + 2 + 3 + 4 + 5 + 6 = 21
32 ! 1 + 2 + 3 + 4 + 5 = 15
33 ! 1 + 2 + 3 + 4 = 10 *** not divisible by 3 ***
35 : euler041 ( -- answer )
36 { 7 6 5 4 3 2 1 } all-permutations
37 [ digits>number ] map [ prime? ] find nip ;
39 ! [ euler041 ] 100 ave-time
40 ! 64 ms ave run time - 4.22 SD (100 trials)