10 lines
1006 B
Markdown
10 lines
1006 B
Markdown
This could be the first problem with prime numbers but without a prime sieve.
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We iterate through the numbers from `1488` to `3340` and search for palindromes.
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To speed up the palindrome calculation we calculate the product of each digit plus two and compare the product of our three numbers.
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This is only an approximation, but a rather good one. In tested the numbers from `0` to `100 000` and there were **zero** failures.
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So now we've got the numbers where `digit_product(p) == digit_product(p+3330) == digit_product(p+6660)` (in fact there are only 40 of these).
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We then use a simple primality test to check if all three numbers are prime.
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The primality test is basically a port of the [wikipedia](http://en.wikipedia.org/wiki/Primality_test) version to befunge. Wit it we only have to do `n/6` divisions to test a number `n` for primality.
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All in all tis leads to a fast, small and not very grid-intensive program (Only one field is used, *and only as a temporary storage to swap three values*). |