A275940 a(n) = A000005(A023194(n)).

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, 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, 3, 11, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7

Offset

1,1

Links

Table of n, a(n) for n=1..88.

Example

a(5) = A000005(A023194(5)) = A000005(25) = 3.

Mathematica

DivisorSigma[0, #] &@ Prepend[Select[Range[5000]^2, PrimeQ[DivisorSigma[1, #]] &], 2] (* Michael De Vlieger, Aug 14 2016, after Harvey P. Dale at A023194 *)

Prog

(PARI) lista(nn) = for(n=1, nn, if(isprime(sigma(n)), print1(numdiv(n), ", ")));

Crossrefs

Cf. A000005, A023194.

Sequence in context: A327124 A329277 A117531 * A105555 A066858 A333496

Adjacent sequences: A275937 A275938 A275939 * A275941 A275942 A275943

Keyword

nonn

Author

Altug Alkan, Aug 13 2016

Status

approved