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URL: https://oeis.org/A347108

⇱ A347108 - OEIS

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A347108
a(n) = Sum_{k=1..n} sigma(k)*sigma(2*k), where sigma(n) = A000203(n) is the sum of the divisors of n.
3
3, 24, 72, 177, 285, 621, 813, 1278, 1785, 2541, 2973, 4653, 5241, 6585, 8313, 10266, 11238, 14787, 15987, 19767, 22839, 25863, 27591, 35031, 37914, 42030, 46830, 53550, 56250, 68346, 71418, 79419, 86331, 93135, 100047, 117792, 122124, 130524, 139932, 156672
OFFSET
1,1
FORMULA
a(n) ~ 2*zeta(3)*n^3.
MATHEMATICA
Accumulate[Table[DivisorSigma[1, k] * DivisorSigma[1, 2*k], {k, 1, 100}]]
PROG
(PARI) a(n) = sum(k=1, n, sigma(k)*sigma(2*k)); \\ Michel Marcus, Aug 18 2021
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Aug 18 2021
STATUS
approved