A359168 - OEIS

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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

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

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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