A155723 Numbers k such that 2*k + 9 is not prime.

0, 3, 6, 8, 9, 12, 13, 15, 18, 20, 21, 23, 24, 27, 28, 30, 33, 34, 36, 38, 39, 41, 42, 43, 45, 48, 51, 53, 54, 55, 56, 57, 58, 60, 62, 63, 66, 67, 68, 69, 72, 73, 75, 76, 78, 80, 81, 83, 84, 87, 88, 89, 90, 93, 96, 97, 98, 99, 100, 102, 103, 104, 105, 106, 108, 111, 113, 114

Offset: 1

Author

Vincenzo Librandi, Jan 25 2009

Keywords

• nonn
• easy

Comments

2*A155724(m,n) + 9 = (2n+1)*(2m+1) are not prime and create entries of this form. Also, one less than the associate entry in A153053, two less than the associated A153052. - R. J. Mathar, Jan 05 2011

Examples

			Distribution of the terms in the following triangular array:
   0;
   3,  8;
   6, 13, 20;
   9, 18, 27,  36;
  12, 23, 34,  45,  56;
  15, 28, 41,  54,  67,  80;
  18, 33, 48,  63,  78,  93, 108;
  21, 38, 55,  72,  89, 106, 123, 140;
  24, 43, 62,  81, 100, 119, 138, 157, 176;
  27, 48, 69,  90, 111, 132, 153, 174, 195, 216;
  30, 53, 76,  99, 122, 145, 168, 191, 214, 237, 260;
  33, 58, 83, 108, 133, 158, 183, 208, 233, 258, 283, 308;
  36, 63, 90, 117, 144, 171, 198, 225, 252, 279, 306, 333, 360;
  etc.
the values of (2*h*k + k + h - 4) with h >= k >= 1. - _Vincenzo Librandi_, Jan 16 2013
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A155724, A155722.

Programs

Magma

[n: n in [0..115]| not IsPrime(2*n+9)]; // Vincenzo Librandi, Mar 01 2012

Mathematica

Select[Range[0,80],!PrimeQ[2*#+9]&] (* Vincenzo Librandi, Mar 01 2012 *)