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

Author

Altug Alkan, Aug 13 2016

Keywords

• nonn

Comments

All the terms are primes. - Amiram Eldar, Jan 25 2025

Examples

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

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005, A023194.

Programs

Mathematica

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

PARI

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