A320941 - OEIS

A320941

Expansion of Sum_{k>=1} x^k*(1 + x^k)/(1 - x^k)^4.

1, 6, 15, 36, 56, 111, 141, 240, 300, 446, 507, 791, 820, 1161, 1310, 1736, 1786, 2505, 2471, 3346, 3466, 4307, 4325, 5895, 5581, 7026, 7230, 8905, 8556, 11246, 10417, 13176, 13050, 15476, 15106, 19391, 17576, 21495, 21374, 25690, 23822, 30162, 27435, 33707, 32990, 37841, 35721

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OFFSET

1,2

COMMENTS

Inverse Möbius transform of square pyramidal numbers (A000330).

LINKS

Table of n, a(n) for n=1..47.

N. J. A. Sloane, Transforms

FORMULA

G.f.: Sum_{k>=1} A000330(k)*x^k/(1 - x^k).

a(n) = Sum_{d|n} d*(d + 1)*(2*d + 1)/6.

a(n) = (A000203(n) + 3*A001157(n) + 2*A001158(n))/6.