A193072 Odd numbers N for which numerator(sigma(N^2)/N^2) is prime but sigma(N^2) is composite.

39, 507, 2379, 6591, 13167, 29511, 148955, 1672209, 8852259, 212370543, 1929229929

Offset

1,1

Comments

a(12) > 10^10. - Lucas A. Brown, Apr 12 2021

Links

Table of n, a(n) for n=1..11.

Lucas A. Brown, A193072.py

Prog

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

Crossrefs

Intersection of A193066 and A193071.

Sequence in context: A357958 A229517 A254871 * A077454 A142976 A200409

Adjacent sequences: A193069 A193070 A193071 * A193073 A193074 A193075

Keyword

nonn,hard,more

Author

M. F. Hasler, Jul 15 2011

Extensions

a(8)-a(10) from Donovan Johnson, Sep 19 2011

a(11) from Lucas A. Brown, Apr 12 2021

Status

approved