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A091022 Semiprimes with semiprime indices. 8

%I

%S 10,15,25,26,38,39,58,62,74,77,94,95,106,118,119,141,145,155,166,177,

%T 178,194,203,213,219,235,254,265,267,274,291,298,299,301,329,346,362,

%U 377,381,386,391,393,411,422,427,454,458,466,471,473,502,514,515,519

%N Semiprimes with semiprime indices.

%C Semiprime of semiprime of n: a(n) = A001358(A001358(n)). - _Jonathan Vos Post_, Apr 29 2005

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

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

%o (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

%Y Cf. A001358, A007097.

%K nonn

%O 1,1

%A _Zak Seidov_, Feb 24 2004

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Last modified September 30 18:12 EDT 2020. Contains 337440 sequences. (Running on oeis4.)