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

Author

Zak Seidov, Feb 24 2004

Keywords

• nonn

Comments

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

Examples

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

Crossrefs

Cf. A001358, A007097.

Programs

Mathematica

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

PARI

upto(limit)={ my(spr=select(x->bigomega(x)==2,[1..limit]), n=1); while(spr[n]<#spr, n++); vecextract(spr,spr[1..n]) } \\ R. J. Mathar, May 23 2006