A130699 Numbers n for which neither 2n-3 nor 2n+3 are primes.

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

Author

W. Neville Holmes, Jul 11 2007

Keywords

• easy
• nonn

Examples

			Not 5 because 7 and 13 are prime, but 6 because neither 9 nor 15 are primes.
		

Crossrefs

Cf. A104278.

Programs

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 *)

PARI

isok(n) = !isprime(2*n-3) && !isprime(2*n+3) \\ Michel Marcus, Jul 11 2013

Extensions

Missing term 24 added by Michel Marcus, Jul 11 2013