Special neighbor primes: Difference between revisions
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Catskill549 (talk | contribs) (added AWK) |
(→{{header|ALGOL 68}}: Use ALGOL 68-primes) |
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=={{header|ALGOL 68}}== |
=={{header|ALGOL 68}}== |
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{{libheader|ALGOL 68-primes}} |
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<lang algol68>BEGIN # find adjacent primes p1, p2 such that p1 + p2 - 1 is also prime # |
<lang algol68>BEGIN # find adjacent primes p1, p2 such that p1 + p2 - 1 is also prime # |
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INT max prime = 100; |
INT max prime = 100; |
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# sieve the primes to max prime * 2 # |
# sieve the primes to max prime * 2 # |
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PR read "primes.incl.a68" PR |
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[ 1 : max prime * 2 ]BOOL prime; |
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[]BOOL prime ( max prime * 2 ); |
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FOR i FROM 3 BY 2 TO UPB prime DO prime[ i ] := TRUE OD; |
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FOR i FROM 4 BY 2 TO UPB prime DO prime[ i ] := FALSE OD; |
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FOR i FROM 3 BY 2 TO ENTIER sqrt( UPB prime ) DO |
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IF prime[ i ] THEN FOR s FROM i * i BY i + i TO UPB prime DO prime[ s ] := FALSE OD FI |
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OD; |
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# count the primes up to max prime # |
# count the primes up to max prime # |
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INT p count := 0; FOR i TO max prime DO IF prime[ i ] THEN p count +:= 1 FI OD; |
INT p count := 0; FOR i TO max prime DO IF prime[ i ] THEN p count +:= 1 FI OD; |
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( 73 + 79 ) - 1 = 151 |
( 73 + 79 ) - 1 = 151 |
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</pre> |
</pre> |
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=={{header|AWK}}== |
=={{header|AWK}}== |
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<lang AWK> |
<lang AWK> |
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