Primes which contain only one odd digit: Difference between revisions
Primes which contain only one odd digit (view source)
Revision as of 22:44, 11 September 2023
, 8 months ago→{{header|Quackery}}: made more efficient
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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.
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>.
<syntaxhighlight lang="Quackery"> [ [] swap
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5 5 ** times
[ i^ evendigits
' [ 1 3
[ over +
dup isprime iff
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else drop ]
drop ]
5 swap 1 stuff
dup say "Qualifying primes < 1000:"
dup findwith [ 999 > ] [ ]
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