A125215 Semiprimes s such that s-/+2 are primes.

9, 15, 21, 39, 69, 111, 129, 309, 381, 489, 501, 771, 879, 939, 1011, 1299, 1569, 2271, 2391, 2661, 2859, 3039, 3189, 3459, 3849, 3909, 3921, 4449, 4791, 4971, 5001, 5079, 5169, 5349, 5739, 6009, 6999, 7041, 7671, 8691, 8781, 9201, 10599, 11469, 11829

Offset: 1

Author

Zak Seidov, Nov 24 2006

Keywords

• nonn

Comments

All terms are multiples of 3, a(n) = 3*A125272(n). - Zak Seidov, May 06 2013

Examples

			9 = 3^2 is a term since it is a semiprime, and both 9 - 2 = 7 and 9 + 2 = 11 are primes.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A125272.

Programs

Mathematica

Reap[Do[p=Prime[i];If[PrimeQ[p+4]&&Total[Last/@FactorInteger[p+2]]==2,Sow[p+2]],{i,2*10^3}]][[2,1]]