A153170 Numbers k such that 3*k + 2 is not prime.

2, 4, 6, 8, 10, 11, 12, 14, 16, 18, 20, 21, 22, 24, 25, 26, 28, 30, 31, 32, 34, 36, 38, 39, 40, 41, 42, 44, 46, 47, 48, 50, 51, 52, 53, 54, 56, 58, 60, 61, 62, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 78, 80, 81, 82, 84, 86, 88, 90, 91, 92, 94, 95, 96, 98, 99, 100, 101, 102

Offset: 1

Author

Vincenzo Librandi, Dec 20 2008

Keywords

• nonn
• easy

Comments

Contains the positive even numbers (A005843) and the odd numbers of the form 2*A059324(.) + 1. - R. J. Mathar, Nov 27 2010

Numbers k such that (3*k)!/(3*k + 2) is an integer. - Peter Bala, Jan 25 2017

Examples

			Distribution of the odd terms in the following triangular array:
  *;
  *,   *;
  *,  11,   *;
  *,   *,   *,   *;
  *,   *,  25,   *,   *;
  *,  21,   *,   *,  47,   *;
  *,   *,   *,   *,   *,   *,   *;
  *,   *,  39,   *,   *,  73,   *,   *;
  *,  31,   *,   *,  69,   *,   *, 107,   *;
  *,   *,   *,   *,   *,   *,   *,   *,   *,   *;
  *,   *,  53,   *,   *,  99,   *,   *, 145,   *,   *;
  *,  41,   *,   *,  91,   *,   *, 141,   *,   *, 191,   *;
etc., where * marks the noninteger values of (4*h*k + 2*k + 2*h - 1)/3 with h >= k >= 1. - _Vincenzo Librandi_, Jan 15 2013
		

Links

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

Crossrefs

Cf. A024893, A014076, A045751, A095277, A153088, A153329, A153343.

Programs

Magma

[n: n in [1..110] | not IsPrime(3*n + 2)]; // Vincenzo Librandi, Oct 11 2012

Maple

for n from 0 to 100 do
if irem(factorial(3*n), 3*n+2) = 0 then print(n); end if;
end do: # Peter Bala, Jan 25 2017

Mathematica

Select[Range[1, 200], !PrimeQ[3*# + 2] &] (* Vincenzo Librandi, Oct 11 2012 *)

PARI

for(n=1,200,if(!isprime(3*n+2), print1(n,", "))) \\  Joerg Arndt, Nov 27 2010

Extensions

Edited by N. J. A. Sloane, Jun 23 2010