A153085 Numbers k such that 4*k + 5 is not prime.

1, 4, 5, 7, 10, 11, 13, 15, 16, 18, 19, 20, 22, 25, 28, 29, 30, 31, 32, 34, 35, 37, 39, 40, 41, 43, 45, 46, 49, 50, 51, 52, 53, 54, 55, 58, 60, 61, 62, 64, 65, 67, 70, 71, 73, 74, 75, 76, 79, 80, 81, 82, 84, 85, 88, 89, 90, 91, 93, 94, 95, 97, 100, 102, 103, 105, 106

Offset

1,2

Comments

Let p=2n+1 be an odd number, then A140869(n,n) = (p^2-5)/4 = A028387(n-1).

One less than the associated entry in A045751: a(n) = A045751(n+1)-1. - R. J. Mathar, Jan 05 2011

Links

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

Example

Triangle begins:
1;
*, 5;
4, *, 11;
*, 10, *, 19;
7, *, 18, *, 29;
*, 15, *, 28, *, 41;
where * mark the entries in A140869 which are non-integer if floor(.) is not applied there.

Mathematica

Select[Range[200], !PrimeQ[4 # + 5] &] (* Vincenzo Librandi, Oct 15 2012 *)

Prog

(Magma) [n: n in [1..120] | not IsPrime(4*n + 5)]; // Vincenzo Librandi, Oct 15 2012

Crossrefs

Cf. A028387, A045751, A111215, A140869.

Sequence in context: A231575 A335001 A368659 * A047259 A287658 A039577

Adjacent sequences: A153082 A153083 A153084 * A153086 A153087 A153088

Keyword

nonn

Author

Vincenzo Librandi, Dec 18 2008

Status

approved