A395339 - OEIS

A395339

a(n) = (2*n)! * [x^(2*n)] cosh(x) * cos(x)^2.

1, -1, -3, 59, -263, 119, 5877, -38221, 82417, 461039, -4826643, 17433899, 16062697, -532223641, 2791774437, -3445055581, -49124027423, 380870554079, -1057122638883, -3179028018661, 45502234084057, -193537704037801, 23670372125397, 4696420368192659, -28770281512290863

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..24.

Index entries for linear recurrences with constant coefficients, signature (-5,-19,25).

FORMULA

a(n) = (Re((1+2*i)^(2*n)) + 1)/2, where i = sqrt(-1).

G.f.: (1+4*x+11*x^2)/((1-x) * (1+6*x+25*x^2)).

a(n) = -5*a(n-1) - 19*a(n-2) + 25*a(n-3).

PROG

(PARI) a(n) = (real((1+2*I)^(2*n))+1)/2;