A120382 Even numbers k such that 3*k-1 and 3*k+1 are not prime.

40, 48, 62, 68, 72, 82, 96, 100, 108, 114, 138, 142, 158, 172, 176, 178, 184, 194, 208, 212, 222, 232, 238, 260, 264, 268, 272, 278, 282, 290, 298, 300, 308, 320, 334, 342, 348, 352, 358, 360, 378, 380, 382, 386, 392, 402, 414, 418, 422, 424, 438, 444, 446, 448, 450

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = 2*A060461(n). - Michel Marcus, Sep 15 2019

Maple

remove(k -> isprime(3*k-1) or isprime(3*k+1), [seq(k, k=2..1000, 2)]); # Robert Israel, Sep 30 2024

Mathematica

Select[Range[2, 450, 2], !PrimeQ[3#-1]&&!PrimeQ[3#+1]&] (* James C. McMahon, Sep 30 2024 *)

Prog

(PARI) isok(n) = !(n%2) && !isprime(3*n-1) && !isprime(3*n+1); \\ Michel Marcus, Sep 15 2019

Crossrefs

Cf. A060461.

Sequence in context: A197734 A114839 A179435 * A290017 A062909 A167327

Adjacent sequences: A120379 A120380 A120381 * A120383 A120384 A120385

Keyword

easy,nonn

Author

Pierre CAMI, Jun 29 2006

Extensions

More terms from Michel Marcus, Sep 15 2019

Status

approved