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A143834 Numbers k such that 2k^2 - 1 is not prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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 A102183

Adjacent sequences:  A143831 A143832 A143833 * A143835 A143836 A143837

KEYWORD

nonn

AUTHOR

Artur Jasinski, Sep 02 2008

STATUS

approved

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Last modified December 13 23:14 EST 2019. Contains 329974 sequences. (Running on oeis4.)