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

1,1

Links

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A024903.

Sequence in context: A138204 A080645 A024413 * A330945 A153167 A227187

Adjacent sequences: A153344 A153345 A153346 * A153348 A153349 A153350

Keyword

nonn,easy

Author

Vincenzo Librandi, Dec 24 2008

Extensions

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

Status

approved