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A130699
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Numbers n for which neither 2n-3 nor 2n+3 are primes.
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1
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6, 9, 12, 15, 18, 21, 24, 26, 27, 30, 33, 36, 39, 42, 44, 45, 48, 51, 54, 57, 59, 60, 61, 63, 66, 69, 72, 75, 78, 79, 81, 84, 86, 87, 90, 93, 96, 99, 102, 103, 105, 106, 108, 109, 111, 114, 117, 120, 123, 125, 126, 128, 129, 131, 132, 135, 138, 141, 144, 146
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OFFSET
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2,1
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LINKS
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EXAMPLE
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Not 5 because 7 and 13 are prime, but 6 because neither 9 nor 15 are primes.
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MATHEMATICA
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Select[Range[200], NoneTrue[2#+{3, -3}, PrimeQ]&] (* The program uses the NoneTrue function from Mathematica version 10 *) (* Harvey P. Dale, Nov 12 2014 *)
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PROG
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(PARI) isok(n) = !isprime(2*n-3) && !isprime(2*n+3) \\ Michel Marcus, Jul 11 2013
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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