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A130699
Numbers n for which neither 2n-3 nor 2n+3 are primes.
1
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
OFFSET
2,1
EXAMPLE
Not 5 because 7 and 13 are prime, but 6 because neither 9 nor 15 are primes.
MATHEMATICA
Select[Range[200], NoneTrue[2#+{3, -3}, PrimeQ]&] (* The program uses the NoneTrue function from Mathematica version 10 *) (* Harvey P. Dale, Nov 12 2014 *)
PROG
(PARI) isok(n) = !isprime(2*n-3) && !isprime(2*n+3) \\ Michel Marcus, Jul 11 2013
CROSSREFS
Cf. A104278.
Sequence in context: A189728 A214777 A239310 * A099862 A014407 A315952
KEYWORD
easy,nonn
AUTHOR
W. Neville Holmes, Jul 11 2007
EXTENSIONS
Missing term 24 added by Michel Marcus, Jul 11 2013
STATUS
approved