A129926 Semiprimes n such that 3*n - 2 is a prime.

15, 21, 25, 33, 35, 51, 55, 65, 77, 91, 93, 95, 111, 123, 133, 141, 145, 155, 183, 201, 203, 205, 215, 221, 237, 247, 253, 287, 295, 303, 323, 341, 355, 365, 377, 391, 411, 413, 417, 427, 485, 497, 511, 515, 517, 527, 533, 537, 543, 553, 565, 581, 583, 597

Offset

1,1

Comments

Indices of 3-almost prime octagonal numbers.

Subset of A001358. - R. J. Mathar, Jun 07 2007

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Maple

isA001358 := proc(n) if numtheory[bigomega](n) = 2 then true ; else false ; end ; end: isA129926 := proc(n) if isA001358(n) then isprime(3*n-2) ; else false ; fi ; end: for n from 1 to 1000 do if isA129926(n) then printf("%d, ", n) ; fi ; od ; # R. J. Mathar, Jun 07 2007

Prog

(PARI) list(lim)=my(v=List(), n); forprime(p=2, lim\2, forprime(q=2, min(lim\p, p), n=p*q; if(isprime(3*n-2), listput(v, n)))); Set(v) \\ Charles R Greathouse IV, Jan 31 2017

Crossrefs

Sequence in context: A156063 A181780 A273061 * A020204 A280389 A057489

Adjacent sequences: A129923 A129924 A129925 * A129927 A129928 A129929

Keyword

nonn

Author

Giovanni Teofilatto, Jun 06 2007

Extensions

More terms from R. J. Mathar, Jun 07 2007

Status

approved