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A125215 Semiprimes s such that s-/+2 are primes. 4
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 29 05:53 EST 2020. Contains 338756 sequences. (Running on oeis4.)