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A259695 a(n) = Sum(k^7*sigma(k)*sigma(n-k),k=1..n-1). 1
0, 1, 387, 9904, 142475, 850500, 5287786, 19400960, 68736681, 210682950, 565317445, 1328193216, 3163440917, 6945663368, 13045807350, 26914795520, 48673795956, 89900901837, 149363037975, 262436871200, 409003474320, 711715515852, 1035199173422, 1683466675200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

This was formerly A001480.

LINKS

Colin Barker, Table of n, a(n) for n = 1..1000

J. Touchard, On prime numbers and perfect numbers, Scripta Math., 129 (1953), 35-39. [Annotated scanned copy]

MAPLE

S:=(n, e)->add(k^e*sigma(k)*sigma(n-k), k=1..n-1); f:=e->[seq(S(n, e), n=1..30)]; f(7);

MATHEMATICA

Table[Sum[k^7 DivisorSigma[1, k]DivisorSigma[1, n-k], {k, n-1}], {n, 30}] (* Harvey P. Dale, Dec 14 2015 *)

PROG

(PARI) a(n) = sum(k=1, n-1, k^7*sigma(k)*sigma(n-k)) \\ Colin Barker, Jul 16 2015

CROSSREFS

Sequence in context: A273383 A038659 A232777 * A223193 A284147 A234178

Adjacent sequences:  A259692 A259693 A259694 * A259696 A259697 A259698

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jul 03 2015

STATUS

approved

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Last modified October 17 12:14 EDT 2019. Contains 328111 sequences. (Running on oeis4.)