A143834 Numbers k such that 2k^2 - 1 is not prime.

1, 5, 9, 12, 14, 16, 19, 20, 23, 26, 27, 29, 30, 31, 32, 33, 35, 37, 40, 44, 47, 48, 51, 53, 54, 55, 57, 58, 60, 61, 65, 66, 67, 68, 70, 71, 72, 74, 75, 77, 78, 79, 82, 83, 84, 86, 88, 89, 90, 93, 94, 96, 97, 99, 100, 101, 103, 104, 105, 106, 107, 110, 111, 114, 116, 117

Offset

1,2

Comments

Complement of A066049.

Links

Table of n, a(n) for n=1..66.

Mathematica

p = 2; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], NULL, AppendTo[a, x]], {x, 1, 1000}]; a
Select[Range[120], !PrimeQ[2#^2-1]&] (* Harvey P. Dale, Mar 14 2018 *)

Prog

(Magma) [n: n in [1..120]| not IsPrime(2*n^2-1)] // Vincenzo Librandi, Jan 28 2011

Crossrefs

Cf. A066436, A066049, A090686, A090684, A143826, A143827, A143828, A143829, A143830, A143831, A143833.

Sequence in context: A287456 A123574 A314611 * A314612 A314613 A356462

Adjacent sequences: A143831 A143832 A143833 * A143835 A143836 A143837

Keyword

nonn

Author

Artur Jasinski, Sep 02 2008

Status

approved