A072864 Numbers m such that the smallest k dividing sigma(k*m^2) is equal to 3.

7, 13, 14, 19, 21, 26, 28, 31, 35, 37, 38, 39, 42, 43, 52, 56, 57, 61, 62, 63, 65, 67, 70, 73, 74, 76, 77, 78, 79, 84, 86, 91, 93, 95, 97, 103, 104, 105, 109, 111, 112, 114, 117, 119, 122, 124, 126, 127, 129, 130, 133, 134, 139, 140, 143, 146, 148, 151, 152, 154

Offset: 1

Author

Benoit Cloitre, Jul 27 2002

Keywords

• easy
• nonn

Comments

Sequence contains primes of the form 6x+1 (A002476) and multiples of those primes, except (6x+1)^2. If x is not in the sequence, the smallest k dividing sigma(k*x^2) is equal to 6.

Crossrefs

Cf. A049605.

Programs

PARI

isok(n) = A049605(n^2) != 6; \\ Michel Marcus, Nov 21 2013