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A091022 Semiprimes with semiprime indices. 8
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 (list; graph; refs; listen; history; text; internal format)
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 * A133372 A100916 A001750

Adjacent sequences:  A091019 A091020 A091021 * A091023 A091024 A091025

KEYWORD

nonn

AUTHOR

Zak Seidov, Feb 24 2004

STATUS

approved

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Last modified August 12 23:19 EDT 2020. Contains 336440 sequences. (Running on oeis4.)