A153049 Numbers n such that 2*n - 13 is not a prime.

7, 11, 14, 17, 19, 20, 23, 24, 26, 29, 31, 32, 34, 35, 38, 39, 41, 44, 45, 47, 49, 50, 52, 53, 54, 56, 59, 62, 64, 65, 66, 67, 68, 69, 71, 73, 74, 77, 78, 79, 80, 83, 84, 86, 87, 89, 91, 92, 94, 95, 98, 99, 100, 101, 104, 107, 108, 109, 110, 111, 113, 114, 115, 116

Offset

1,1

Comments

All entries of A163672 are in the sequence because 2*A163672(n,m)-13 = (2n+1)(2m+1) is not prime. - R. J. Mathar, Jan 05 2011

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Example

Distribution of a(n) > 7 in the following triangular array:
11;
14,19;
17,24,31;
20,29,38,47;
23,34,45,56,67;
26,39,52,65,78,91;
29,44,59,74,89,104,119;
32,49,66,83,100,117,134,151;
35,54,73,92,111,130,149,168,187;
38,59,80,101,122,143,164,185,206,227;
41,64,87,110,133,156,179,202,225,248,271;
44,69,94,119,144,169,194,219,244,269,294,319; etc.
which is obtained by (2*h*k + k + h + 7) with h >= k >= 1. - Vincenzo Librandi, Jan 15 2013

Mathematica

Select[Range[7, 200], !PrimeQ[2 # - 13] &] (* Vincenzo Librandi, Oct 15 2012 *)

Prog

(Magma) [n: n in [7..120] | not IsPrime(2*n - 13)]; // Vincenzo Librandi, Oct 15 2012

Crossrefs

Cf. A097363, A163672.

Sequence in context: A356455 A004235 A004236 * A065105 A118797 A080837

Adjacent sequences: A153046 A153047 A153048 * A153050 A153051 A153052

Keyword

nonn,easy

Author

Vincenzo Librandi, Dec 17 2008

Status

approved