A173082 Semiprimes q such that q^2+2 and q^2-2 are also semiprimes.

6, 51, 65, 115, 133, 141, 159, 187, 201, 209, 213, 287, 291, 295, 327, 339, 361, 407, 411, 413, 471, 493, 511, 519, 537, 559, 579, 597, 633, 649, 687, 695, 723, 799, 813, 831, 835, 871, 917, 939, 1007, 1041, 1047, 1079, 1135, 1167, 1189, 1195, 1199, 1227

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Feb 09 2010

Keywords

• nonn

Examples

			6^2-2=34 = 2*17 and 6^2+2=38 = 2*19 are semiprimes derived from the semiprime q=6, so q=6 is in the sequence.
		

Crossrefs

Cf. A001358

Programs

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1,1}||Last/@FactorInteger[n]=={2}; lst={}; Do[If[f[n], a=n^2-2;b=n^2+2;If[f[a]&&f[b],AppendTo[lst,n]]],{n,8!}]; lst

Formula

{A001358(j): A074985(j)-2 in A001358 and A074985(j)+2 in A001358}. [R. J. Mathar, Mar 11 2010]

Extensions

Definition rephrased - R. J. Mathar, Mar 11 2010