A130771 Numbers n not divisible by 3 for which neither 2n-3 nor 2n+3 are primes.

26, 44, 59, 61, 79, 86, 103, 106, 109, 125, 128, 131, 146, 149, 151, 161, 163, 166, 169, 179, 184, 187, 194, 205, 224, 236, 239, 254, 257, 265, 266, 268, 271, 274, 278, 281, 289, 293, 296, 304, 313, 316, 326, 334, 341, 346, 350, 355, 359, 364, 367, 376, 389, 391

Offset

1,1

Comments

This is A130699 with the trivial multiples of 3 removed.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..2500

Example

26 because 2*26+3=55 is not a prime, nor is 2*26-3=49.

Mathematica

Select[Range[400], !Divisible[#, 3]&&NoneTrue[2#+{3, -3}, PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 19 2018 *)

Prog

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

Crossrefs

Cf. A130699, A001651.

Sequence in context: A248404 A280645 A260207 * A217775 A260200 A178100

Adjacent sequences: A130768 A130769 A130770 * A130772 A130773 A130774

Keyword

easy,nonn

Author

W. Neville Holmes, Jul 14 2007

Extensions

Missing term 169 added by Michel Marcus, Jul 11 2013

Status

approved