A359168 Numbers k for which there is an odd number of prime factors (when counted with multiplicity) in k*sigma(k), where sigma is the sum of divisors function.

3, 4, 5, 6, 8, 9, 10, 13, 16, 18, 21, 23, 25, 26, 27, 28, 33, 35, 37, 42, 44, 46, 50, 51, 53, 54, 55, 56, 57, 59, 60, 61, 63, 64, 66, 68, 70, 73, 74, 76, 83, 85, 87, 88, 89, 91, 93, 95, 96, 99, 102, 103, 106, 110, 112, 114, 116, 118, 120, 122, 123, 124, 125, 126, 129, 131, 136, 139, 141, 143, 145, 146

Offset: 1

Author

Antti Karttunen, Dec 19 2022

Keywords

• nonn

Comments

Numbers k such that the parities of A001222(k) and A058063(k) differ.

Links

• Index entries for sequences where odd perfect numbers must occur, if they exist at all
• Index entries for sequences related to sigma(n)

Crossrefs

Positions of -1's in A359166.

Cf. A000203, A001222, A058063, A359167 (complement).

Cf. also A358767, A358768.

Cf. A000396, A005820, A046060, A065997 (subsequences).

Programs

PARI

isA359168(n) = ((bigomega(n)+bigomega(sigma(n)))%2);