8 lines
733 B
Markdown
8 lines
733 B
Markdown
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Perhaps you remember from elementary school that numbers with a digit sum divisible by three is also divisible by three (an so not a prime).
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So our number can't be 9 digits long (digit sum = `45`) nor 8 (digit sum = `36`). Our next best try is a 7-digit palindrome.
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With the [QuickPerm algorithm](http://www.quickperm.org/) we generate all the permutations and test them for their primality.
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This time we don't use a prime sieve, the numbers are just too big and it's faster with a simple naive prime test.
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The rest is just implementation.
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But the resulting code looks imho pretty nice because it really uses the four directions of befunge and often intersects with itself, even though I think that doesn't make it more readable.
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