A358768 Numbers k with an odd number of prime factors (when counted with multiplicity) in sigma(k), the sum of divisors of k.

2, 4, 6, 7, 9, 10, 11, 12, 16, 17, 19, 20, 21, 25, 26, 29, 30, 31, 32, 33, 35, 41, 43, 45, 46, 47, 48, 51, 52, 54, 55, 56, 57, 60, 64, 67, 71, 72, 74, 75, 78, 79, 80, 85, 87, 88, 91, 92, 93, 95, 96, 97, 98, 101, 105, 106, 107, 108, 109, 113, 117, 118, 122, 123, 126, 127, 128, 129, 130, 136, 137, 138

Offset: 1

Author

Antti Karttunen, Dec 19 2022

Keywords

• nonn

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Positions of odd terms in A058063. Positions of -1's in A358766.

Cf. A000203, A001222, A358767 (complement).

Programs

PARI

isA358768(n) = (bigomega(sigma(n))%2);