OFFSET
1,1
COMMENTS
91 = 7*13; 7 and 13 are not 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
With[{nn=50}, Take[Union[Times@@@Subsets[Select[Prime[Range[nn]], !PrimeQ[ 2#+1]&], {2}]], nn]] (* Harvey P. Dale, May 04 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Feb 27 2009
STATUS
approved