OFFSET
0,2
FORMULA
E.g.f.: exp( 2 * (1 - cosh(x)) ) (even powers only).
MATHEMATICA
a[0] = 1; a[n_] := a[n] = -2 Sum[Binomial[2 n - 1, 2 k - 1] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 18}]
nmax = 36; Take[CoefficientList[Series[Exp[2 (1 - Cosh[x])], {x, 0, nmax}], x] Range[0, nmax]!, {1, -1, 2}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Mar 10 2022
STATUS
approved