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

1,2

Links

Table of n, a(n) for n=1..53.

Example

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.

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 *)

Crossrefs

Cf. A174838.

Sequence in context: A228958 A216669 A015633 * A265248 A131661 A321287

Adjacent sequences: A176188 A176189 A176190 * A176192 A176193 A176194

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 11 2010

Extensions

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

Status

approved