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A157344 Semiprimes that are the product of two distinct Sophie Germain primes. 10
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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..54.

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 * A093773 A088708 A174872

Adjacent sequences:  A157341 A157342 A157343 * A157345 A157346 A157347

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

STATUS

approved

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Last modified June 27 11:25 EDT 2017. Contains 288788 sequences.