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%I #7 Aug 16 2016 09:48:46
%S 2,3,3,5,3,7,3,7,3,5,3,13,3,3,3,7,3,3,5,3,17,5,3,3,19,5,3,3,13,3,3,3,
%T 3,3,5,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,5,3,3,3,7,3,3,3,3,3,3,3,3,3,3,
%U 3,11,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,7
%N a(n) = A000005(A023194(n)).
%e a(5) = A000005(A023194(5)) = A000005(25) = 3.
%t DivisorSigma[0, #] &@ Prepend[Select[Range[5000]^2, PrimeQ[DivisorSigma[1, #]] &], 2] (* _Michael De Vlieger_, Aug 14 2016, after _Harvey P. Dale_ at A023194 *)
%o (PARI) lista(nn) = for(n=1, nn, if(isprime(sigma(n)), print1(numdiv(n), ", ")));
%Y Cf. A000005, A023194.
%K nonn
%O 1,1
%A _Altug Alkan_, Aug 13 2016
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