A007638 - OEIS

A007638

Numbers k such that 3*k^2 - 3*k + 23 is composite.
(Formerly M5129)

23, 24, 28, 31, 39, 44, 45, 46, 47, 50, 52, 56, 57, 60, 63, 67, 69, 70, 71, 79, 80, 85, 86, 88, 89, 90, 92, 93, 96, 97, 102, 107, 108, 112, 115, 116, 118, 119, 121, 122, 123, 126, 128, 131, 134, 137, 138, 139, 143, 144, 145, 147, 148, 151, 153, 156, 157, 161, 162

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..3100

H. Dubner, Generalized Cullen numbers, J. Rec. Math., 21 (No. 3, 1989), 190-191. (Annotated scanned copy)

MATHEMATICA

Select[Range[200], !PrimeQ[3 #^2 - 3 # + 23] &] (* Vincenzo Librandi, Jun 08 2017 *)

PROG

(PARI) is(n)=!isprime(3*n^2 - 3*n + 23) \\ Charles R Greathouse IV, Oct 23 2015

(Magma) [n: n in [0..200]| not IsPrime(3*n^2-3*n+23)]; // Vincenzo Librandi, Jun 08 2017

CROSSREFS

Sequence in context: A291511 A062999 A241889 * A031332 A122470 A022393

Adjacent sequences: A007635 A007636 A007637 * A007639 A007640 A007641

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Mira Bernstein, Robert G. Wilson v

STATUS

approved