OFFSET
1,2
COMMENTS
Inverse Möbius transform of square pyramidal numbers (A000330).
LINKS
N. J. A. Sloane, Transforms
FORMULA
MAPLE
a:=series(add(x^k*(1+x^k)/(1-x^k)^4, k=1..100), x=0, 48): seq(coeff(a, x, n), n=1..47); # Paolo P. Lava, Apr 02 2019
MATHEMATICA
nmax = 47; Rest[CoefficientList[Series[Sum[x^k (1 + x^k)/(1 - x^k)^4, {k, 1, nmax}], {x, 0, nmax}], x]]
Table[Sum[d (d + 1) (2 d + 1)/6, {d, Divisors[n]}], {n, 47}]
Table[(DivisorSigma[1, n] + 3 DivisorSigma[2, n] + 2 DivisorSigma[3, n])/6, {n, 47}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Oct 24 2018
STATUS
approved