A130699 - OEIS

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

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OFFSET

2,1

LINKS

Table of n, a(n) for n=2..61.

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

Adjacent sequences: A130696 A130697 A130698 * A130700 A130701 A130702

KEYWORD

easy,nonn

AUTHOR

W. Neville Holmes, Jul 11 2007

EXTENSIONS

Missing term 24 added by Michel Marcus, Jul 11 2013

STATUS

approved