A091022 Semiprimes with semiprime indices.

10, 15, 25, 26, 38, 39, 58, 62, 74, 77, 94, 95, 106, 118, 119, 141, 145, 155, 166, 177, 178, 194, 203, 213, 219, 235, 254, 265, 267, 274, 291, 298, 299, 301, 329, 346, 362, 377, 381, 386, 391, 393, 411, 422, 427, 454, 458, 466, 471, 473, 502, 514, 515, 519

Offset

1,1

Comments

Semiprime of semiprime of n: a(n) = A001358(A001358(n)). - Jonathan Vos Post, Apr 29 2005

Links

Table of n, a(n) for n=1..54.

Example

10 is a member because 10 is 4th semiprime and 4 is a semiprime.

Mathematica

With[{sprs=Select[Range[700], PrimeOmega[#]==2&]}, Flatten[Table[Take[sprs, Take[ sprs, {n}]], {n, 60}]]] (* Harvey P. Dale, Aug 22 2011 *)

Prog

(PARI) A001358()= { local(resul); resul = [4]; for(n=5, 1000, if ( bigomega(n) == 2, resul =concat(resul, n); ); ); return(resul); } { spr=Vec(A001358()); sprlen=(matsize(spr))[2]; for(n=1, sprlen, if( spr[n]>=sprlen, break; ); print1(spr[spr[n]], ", "); ); } - R. J. Mathar, May 23 2006

Crossrefs

Cf. A001358, A007097.

Sequence in context: A057990 A272779 A173477 * A340731 A133372 A100916

Adjacent sequences: A091019 A091020 A091021 * A091023 A091024 A091025

Keyword

nonn

Author

Zak Seidov, Feb 24 2004

Status

approved