A153347 Numbers n>0 such that 7*n-4 is not prime.

2, 4, 6, 7, 8, 10, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 30, 31, 32, 34, 36, 37, 38, 40, 42, 43, 44, 46, 47, 48, 49, 50, 52, 54, 55, 56, 57, 58, 60, 61, 62, 63, 64, 65, 66, 67, 68, 70, 71, 72, 73, 74, 76, 77, 78, 79, 80, 82, 84, 85, 86, 87, 88, 90, 91, 92

Offset: 1

Author

Vincenzo Librandi, Dec 24 2008

Keywords

• nonn
• easy

Examples

			Distribution of the odd terms in the following triangular array:
*;
*,*;
*,*,*;
*,7,*,*;
*,*,*,*,*;
*,*,*,*,21,*;
7,*,*,*,*,*,*;
*,*,*,*,*,*,37,*;
*,*,*,25,*,*,*,*,*;
*,*,*,*,*,*,*,*,*,*;
*,17,*,*,*,*,*,*,63,*,*;
*,*,*,*,*,47,*,*,*,*,*,*;
*,*,*,*,43,*,*,*,*,*,*,97,*;
13,*,*,*,*,*,*,71,*,*,*,*,*,*; etc.
where * marks the non-integer values of (4*h*k + 2*k + 2*h + 5)/7 with h >= k >= 1. - _Vincenzo Librandi_, Jan 17 2013
		

Links

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

Crossrefs

Cf. A024903.

Programs

Magma

[n: n in [1..150] | not IsPrime(7*n-4)]; // Vincenzo Librandi, Jan 13 2013

Mathematica

Select[Range[1, 200], !PrimeQ[7 # - 4]&] (* Vincenzo Librandi, Jan 13 2013 *)

Extensions

Erroneous comment deleted by N. J. A. Sloane, Jun 23 2010