A157344 Semiprimes that are the product of two distinct Sophie Germain primes.

6, 10, 15, 22, 33, 46, 55, 58, 69, 82, 87, 106, 115, 123, 145, 159, 166, 178, 205, 226, 249, 253, 262, 265, 267, 319, 339, 346, 358, 382, 393, 415, 445, 451, 466, 478, 502, 519, 537, 562, 565, 573, 583, 586, 655, 667, 699, 717, 718, 753, 838, 843, 862, 865

Offset

1,1

Comments

6=2*3; 2 and 3 are Sophie Germain primes, 10=2*5; 2 and 5 are Sophie Germain primes, 15=3*5; 3 and 5 are Sophie Germain primes, ...

Links

G. C. Greubel, Table of n, a(n) for n = 1..5000

Mathematica

lst={}; Do[If[Plus@@Last/@FactorInteger[n]==2, a=Length[First/@FactorInteger[n]]; If[a==2, b=First/@FactorInteger[n]; c=b[[1]]; d=b[[2]]; If[PrimeQ[2*c+1]&&PrimeQ[2*d+1], AppendTo[lst, n]]]], {n, 7!}]; lst
nn=100; With[{sgp=Select[Prime[Range[nn]], PrimeQ[2#+1]&]}, Take[ Union[ Select[ Times @@@ Subsets[sgp, {2}], PrimeOmega[#]==2&]], nn]] (* Harvey P. Dale, Nov 22 2012 *)

Crossrefs

Cf. A001358, A005384, A111206, A157342, A006881.

Sequence in context: A022949 A049694 A285766 * A332765 A093773 A088708

Adjacent sequences: A157341 A157342 A157343 * A157345 A157346 A157347

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

Status

approved