OFFSET
1,2
FORMULA
E.g.f.: Sum_{k>=1} A067856(k) * log(cos(x^k)) / k (even powers only).
MATHEMATICA
b[n_, i_] := b[n, i] = If[n == 0, 1, If[i < 1, 0, Sum[Binomial[c[i], j] b[n - i j, i - 1], {j, 0, n/i}]]]; c[n_] := c[n] = {1, 0, -1, 0}[[Mod[n + 1, 4, 1]]]/n! - b[n, n - 1]; a[n_] := (2 n)! c[2 n]; Table[a[n], {n, 1, 16}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 18 2022
STATUS
approved