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A241264 Numbers k such that 2*k^2 + 2*k - 41 is not a prime. 1
4, 13, 20, 24, 26, 30, 31, 32, 35, 36, 37, 38, 40, 41, 43, 47, 49, 51, 54, 55, 60, 62, 63, 64, 67, 70, 71, 72, 73, 75, 76, 78, 79, 81, 82, 84, 85, 88, 89, 92, 94, 97, 98, 100, 102, 105, 108, 109, 111, 112, 113, 114, 115, 117, 118, 119, 120, 122, 123, 124, 125 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..5000

EXAMPLE

13 is in this sequence because 2*13^2 + 2*13 - 41 = 323 = 17*19.

MATHEMATICA

Select[Range[4, 200], ! PrimeQ[2 #^2 + 2 # - 41] &]

PROG

(MAGMA) [n: n in [1..150] | not IsPrime(2*n^2+2*n-41)];

CROSSREFS

Complement of A155771.

Sequence in context: A292363 A119048 A319259 * A066993 A297884 A298289

Adjacent sequences:  A241261 A241262 A241263 * A241265 A241266 A241267

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Apr 20 2014

STATUS

approved

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Last modified October 20 11:18 EDT 2019. Contains 328257 sequences. (Running on oeis4.)