A193066 Odd numbers N such that numerator(sigma(N^2)/N^2) is a prime.

3, 5, 17, 27, 39, 41, 49, 59, 71, 89, 101, 125, 131, 167, 169, 173, 289, 293, 383, 507, 529, 677, 701, 729, 743, 761, 773, 827, 839, 841, 857, 911, 1091, 1097, 1163, 1181, 1193, 1217, 1373, 1427, 1487

Offset: 1

Author

M. F. Hasler, Jul 15 2011

Keywords

• nonn

Comments

Square roots of the terms of A193065. See there for more comments.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[1,1501,2],PrimeQ[Numerator[DivisorSigma[1,#^2]/#^2]]&] (* Harvey P. Dale, Sep 24 2016 *)

PARI

forstep(N=1, 1e7, 2, isprime(numerator(sigma(N^2)/N^2)) && print1(N", "))

Formula

a(n) = A000196(A193065(n)).