OFFSET
1,3
MATHEMATICA
nn = 22; f[x_] := Product[(1 + a[n] x^n/n!), {n, 1, nn}]; sol = SolveAlways[0 == Series[f[x] - 1 - ArcTanh[x], {x, 0, nn}], x]; Table[a[n], {n, 1, nn}] /. sol // Flatten
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 08 2022
STATUS
approved