OFFSET
1,6
COMMENTS
Sum of cubes of divisors of n that are smaller than sqrt(n).
MATHEMATICA
nmax = 77; CoefficientList[Series[Sum[k^3 x^(k (k + 1))/(1 - x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
Table[DivisorSum[n, #^3 &, # < Sqrt[n] &], {n, 77}]
PROG
(PARI) a(n) = sumdiv(n, d, if (d^2 < n, d^3)); \\ Michel Marcus, Dec 02 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 01 2020
STATUS
approved