OFFSET
0,3
FORMULA
a(0) = 1; a(n) = -Sum_{k=1..n} binomial(2*n-1,2*k-1) * A000364(k) * a(n-k).
MATHEMATICA
nmax = 16; Table[(CoefficientList[Series[Exp[1 - Sec[x]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
a[0] = 1; a[n_] := a[n] = -Sum[Binomial[2 n - 1, 2 k - 1] Abs[EulerE[2 k]] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 16}]
PROG
(PARI) a(n) = {polcoef(serlaplace(exp(1 - 1/cos(x + O(x^(2*n + 1))))), 2*n)} \\ Andrew Howroyd, Jan 27 2020
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Jan 27 2020
STATUS
approved