OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..207
FORMULA
G.f. cos(x)/(1 - 3*sin(x)^2) = 1 + 5*x^2/2! + 157*x^4/4! + 12425*x^6/6! + ... - Peter Bala, Feb 06 2017
MAPLE
with(gfun):
series(cos(x)/(1-3*sin(x)^2), x, 30):
L := seriestolist(%):
seq(op(2*i-1, L)*(2*i-2)!, i = 1..floor((1/2)*nops(L)));
# Peter Bala, Feb 06 2017
MATHEMATICA
With[{nmax = 50}, CoefficientList[Series[Cos[x]/(1 - 3*Sin[x]^2), {x, 0, nmax}], x]*Range[0, nmax]!][[1 ;; ;; 2]] (* G. C. Greubel, Mar 29 2018 *)
PROG
(PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x)/(1 - 3*sin(x)^2))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Mar 29 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 06 2009
STATUS
approved