|
%I #11 Feb 02 2018 02:53:12
%S 6,10,15,22,33,46,55,58,69,82,87,106,115,123,145,159,166,178,205,226,
%T 249,253,262,265,267,319,339,346,358,382,393,415,445,451,466,478,502,
%U 519,537,562,565,573,583,586,655,667,699,717,718,753,838,843,862,865
%N Semiprimes that are the product of two distinct Sophie Germain primes.
%C 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, ...
%H G. C. Greubel, <a href="/A157344/b157344.txt">Table of n, a(n) for n = 1..5000</a>
%t 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
%t 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 *)
%Y Cf. A001358, A005384, A111206, A157342, A006881.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Feb 27 2009
|
