A157342 Semiprimes that are the product of two non-Sophie Germain primes.

49, 91, 119, 133, 169, 217, 221, 247, 259, 289, 301, 323, 329, 361, 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, 961, 973, 1003, 1027, 1037, 1043, 1057

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

Keywords

• nonn

Examples

			49 = 7*7, 2*7 + 1 = 15 (not prime);
91 = 7*13, 2*7 + 1 = 15 (not prime), 2*13 + 1 = 27 (not prime); ...
		

Links

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

Crossrefs

Cf. A001358, A005384, A111206.

Programs

Mathematica

lst={};Do[If[Plus@@Last/@FactorInteger[n]==2,a=First/@FactorInteger[n];b=a[[1]];k=0;If[Length[a]==2,c=a[[2]];If[PrimeQ[2*c+1],k=1]];If[ !PrimeQ[2*b+1]&&k==0,AppendTo[lst,n]]],{n,7!}];lst
With[{nn=60},Take[Times@@@Tuples[Select[Prime[Range[nn]],!PrimeQ[ 2#+1]&], 2] // Union,nn]] (* Harvey P. Dale, Feb 15 2017 *)