A176191 Numbers n such that semiprime(n)-1 is prime, where semiprime(n) is A001358.

1, 2, 5, 14, 22, 25, 52, 62, 88, 100, 126, 133, 142, 169, 188, 198, 202, 222, 229, 263, 299, 321, 340, 354, 359, 364, 388, 407, 426, 465, 478, 504, 539, 556, 577, 579, 611, 668, 700, 722, 737, 781, 797, 814, 857, 905, 916, 932, 984, 1033, 1108, 1118, 1148

Offset: 1

Author

Juri-Stepan Gerasimov, Apr 11 2010

Keywords

• nonn

Examples

			a(1)=1 because semiprime(1)-1=3=prime, a(2)=2 because semiprime(2)-1=5=prime, a(3)=5 because semiprime(5)-1=13=prime.
		

Crossrefs

Cf. A174838.

Programs

Mathematica

nn=5000;With[{sps=Select[Range[nn],PrimeOmega[#]==2&]},Transpose[ Select[ Thread[ {sps,Range[ Length[sps]]}],PrimeQ[First[#]-1]&]][[2]]] (* Harvey P. Dale, Jul 19 2011 *)

Extensions

Corrected (478 inserted) by R. J. Mathar, Apr 13 2010