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Twin primes: Difference between revisions
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=={{header|J}}==
<lang j>tp=: 3 : '+/ (*. _2&(|.!.0)) 1 p: i. y'
NB. 3 : '' explicitly define a "monad" (a one-argument function)
NB. i. y list integers up to the provided argument
NB. 1 p: create list of 0s, 1s where those ints are prime
NB. _2&(|.!.0) "shift" that list to the right by two, filling left side with 0
NB. (*. g) y create a "hook". "and" together the original and shifted lists
NB. the result will have a 1 only if that i, and i-2, are both prime
NB. +/ sum the and-ed list (get the number of twin pairs)</lang>
{{out}}
<pre> tp 100
8
tp 1000
35
NB. test larger limits, and get their time/space usage
tp 10000000
58980
timespacex 'tp 10000000'
2.37363 1.50996e8
tp 100000000
440312
timespacex 'tp 100000000'
51.0851 1.20796e9</pre>
=={{header|jq}}==
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