OFFSET
1,12
FORMULA
G.f.: Sum_{k>=1} (2*k - 1)^4 * x^(2*k*(2*k - 1)) / (1 - x^(2*k - 1)).
MATHEMATICA
Table[DivisorSum[n, #^4 &, # < Sqrt[n] && OddQ[#] &], {n, 1, 75}]
nmax = 75; CoefficientList[Series[Sum[(2 k - 1)^4 x^(2 k (2 k - 1))/(1 - x^(2 k - 1)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Aug 21 2021
STATUS
approved