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

1,1

Comments

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

Links

Table of n, a(n) for n=1..72.

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Index entries for sequences related to sigma(n)

Prog

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

Crossrefs

Positions of -1's in A359166.

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

Cf. also A358767, A358768.

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

Sequence in context: A063977 A371663 A290136 * A332739 A306588 A353300

Adjacent sequences: A359165 A359166 A359167 * A359169 A359170 A359171

Keyword

nonn

Author

Antti Karttunen, Dec 19 2022

Status

approved