Primes which contain only one odd digit: Difference between revisions
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<code>evendigits</code> returns the nth number which has only even digits and ends with zero. There are self-evidently 5^5 of them less than 1000000. |
<code>evendigits</code> returns the nth number which has only even digits and ends with zero. There are self-evidently 5^5 of them less than 1000000. |
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We know that the only prime ending with a 5 is 5. So we can omit generating candidate numbers that end with a 5, and stuff the 5 into the right place in the nest (i.e. as item #1; item #0 will be 3) afterwards. This explains the lines <code>' [ 1 3 7 9 ] witheach</code> and <code>5 swap 1 stuff</code>. |
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<syntaxhighlight lang="Quackery"> [ [] swap |
<syntaxhighlight lang="Quackery"> [ [] swap |
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5 5 ** times |
5 5 ** times |
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[ i^ evendigits |
[ i^ evendigits |
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' [ 1 3 |
' [ 1 3 7 9 ] witheach |
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[ over + |
[ over + |
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dup isprime iff |
dup isprime iff |
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else drop ] |
else drop ] |
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drop ] |
drop ] |
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5 swap 1 stuff |
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dup say "Qualifying primes < 1000:" |
dup say "Qualifying primes < 1000:" |
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dup findwith [ 999 > ] [ ] |
dup findwith [ 999 > ] [ ] |
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