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

1,1

Comments

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

Links

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

Example

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

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]]

Crossrefs

Cf. A001358, A125272.

Sequence in context: A072569 A072572 A029708 * A102739 A124622 A189051

Adjacent sequences: A125212 A125213 A125214 * A125216 A125217 A125218

Keyword

nonn

Author

Zak Seidov, Nov 24 2006

Status

approved