OFFSET
1,2
COMMENTS
Inverse Euler transform of tetrahedral numbers (A000292).
FORMULA
-1 + Product_{n>=1} 1/(1 - x^n)^a(n) = g.f. of A000292.
MATHEMATICA
nmax = 36; CoefficientList[Series[Sum[MoebiusMu[k] Log[1 + x^k/(1 - x^k)^4]/k, {k, 1, nmax}], {x, 0, nmax}], x] // Rest
nmax = 50; s = ConstantArray[0, nmax]; Do[s[[j]] = j^2*(j + 1)*(j + 2)/6 - Sum[s[[d]]*(j - d)*(j - d + 1)*(j - d + 2)/6, {d, 1, j - 1}], {j, 1, nmax}]; Table[Sum[MoebiusMu[k/d]*s[[d]], {d, Divisors[k]}]/k, {k, 1, nmax}] (* Vaclav Kotesovec, Aug 10 2019 *)
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 18 2019
STATUS
approved