A157345 Semiprimes that are the product of two distinct non-Sophie Germain primes.

91, 119, 133, 217, 221, 247, 259, 301, 323, 329, 403, 413, 427, 469, 481, 497, 511, 527, 553, 559, 589, 611, 629, 679, 703, 707, 721, 731, 749, 763, 767, 793, 799, 817, 871, 889, 893, 923, 949, 959, 973, 1003, 1027, 1037, 1043, 1057, 1099, 1121, 1139, 1141

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

Cf. A001358, A005384, A111206, A157342, A006881, A157344.

Sequence in context: A161945 A140389 A236845 * A092125 A005935 A020307

Adjacent sequences: A157342 A157343 A157344 * A157346 A157347 A157348

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

Status

approved