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A279917

a(n) = Sum_{k=1..n-1} sigma_5(k)*sigma_7(n-k).

0, 1, 162, 6689, 121250, 1296406, 9613604, 54550049, 252178758, 992204376, 3424910566, 10615778966, 30047257318, 78751366604, 193075366412, 446840757793, 982597838280, 2066025009763, 4171924730922, 8127978871064, 15324653827568, 28059983210370

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OFFSET

1,3

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = (sigma_13(n)+20*sigma_7(n)-21*sigma_5(n))/10080.

MATHEMATICA

a[n_] := (DivisorSigma[13, n] + 20 * DivisorSigma[7, n] - 21 * DivisorSigma[5, n]) / 10080; Array[a, 25] (* Amiram Eldar, Jan 07 2025 *)

PROG

(PARI) a(n) = {my(f = factor(n)); (sigma(f, 13) + 20 * sigma(f, 7) - 21 * sigma(f, 5)) / 10080; } \\ Amiram Eldar, Jan 07 2025

CROSSREFS

Cf. A001160, A013955, A013961, A279888.

Sequence in context: A035746 A285046 A022151 * A291131 A209965 A230837

Adjacent sequences: A279914 A279915 A279916 * A279918 A279919 A279920

KEYWORD

nonn

AUTHOR

Seiichi Manyama, Dec 23 2016

STATUS

approved

URL: https://oeis.org/A279917

⇱ A279917 - OEIS