OFFSET
1,1
FORMULA
MATHEMATICA
Table[-(1/n) Sum[EulerPhi[n/d] (-3)^d, {d, Divisors[n]}], {n, 1, 30}]
nmax = 30; CoefficientList[Series[Sum[EulerPhi[k] Log[1 + 3 x^k]/k, {k, 1, nmax}], {x, 0, nmax}], x] // Rest
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Apr 16 2021
STATUS
approved