Sexy primes: Difference between revisions
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=={{header|J}}== |
=={{header|J}}== |
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A brute force approach finds primes in the task range which are preceded by primes with appropriate offsets: |
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<syntaxhighlight lang=J> #sp2=: (#~ 1 p: _6+]) p1=:i.&.(p:inv) 1000035 NB. pairs |
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16386 |
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(_6*i.-2)+/_5{.sp2 |
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999371 999431 999721 999763 999953 |
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999377 999437 999727 999769 999959 |
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#sp3=: (#~ 1 p: _12+]) sp2 NB. triplets |
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2900 |
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(_6*i.-3)+/_5{.sp3 |
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997427 997541 998071 998617 998737 |
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997433 997547 998077 998623 998743 |
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997439 997553 998083 998629 998749 |
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#sp4=: (#~ 1 p: _18+]) sp3 NB. quads |
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325 |
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(_6*i.-5)+/_5{.sp4 |
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977345 983765 986125 990365 997085 |
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977351 983771 986131 990371 997091 |
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977357 983777 986137 990377 997097 |
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977363 983783 986143 990383 997103 |
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977369 983789 986149 990389 997109 |
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#sp5=: (#~ 1 p: _24+]) sp4 NB. quint |
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1 |
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(_6*i.5)+/sp5 |
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29 |
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23 |
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17 |
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11 |
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5 |
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#unp=: p1-.,sp2-/0 6 NB. unsexy |
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48628 |
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_10{.unp |
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999863 999883 999907 999917 999931 999961 999979 999983 1000003 1000033 |
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</syntaxhighlight> |
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And here's a different approach: |
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<syntaxhighlight lang="j">NB. Primes Not Greater Than (the input) |
<syntaxhighlight lang="j">NB. Primes Not Greater Than (the input) |
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NB. The 1 _1 p: ... logic here allows the input value to |
NB. The 1 _1 p: ... logic here allows the input value to |
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