A107987 Odd composite numbers of the form p+2 where p is prime.

9, 15, 21, 25, 33, 39, 45, 49, 55, 63, 69, 75, 81, 85, 91, 99, 105, 111, 115, 129, 133, 141, 153, 159, 165, 169, 175, 183, 195, 201, 213, 225, 231, 235, 243, 253, 259, 265, 273, 279, 285, 295, 309, 315, 319, 333, 339, 351, 355, 361, 369, 375, 381, 385, 391, 399

Offset: 1

Author

Cino Hilliard, Jun 13 2005

Keywords

• easy
• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A049591, A067774.

Programs

Mathematica

DeleteCases[Prime[Range[2,80]]+2,?PrimeQ] (* _Harvey P. Dale, Aug 15 2013 *)

PARI

sum2pr(n) = \\ Composite numbers of form p+2.
{ c=0; cp=0; forprime(x=3, n, cp++; y=x+2; if(isprime(y)==0, c++; print1(y",") ) ); print(); print(c/cp+.) }

Formula

a(n) = A049591(n) + 2 = A067774(n+1) + 2. - Amiram Eldar, Jul 05 2024