OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..240
FORMULA
a(n) = 2*Sum_{m=1..n-1} binomial(2*n,2*m)*Sum_{j=0..n-m} binomial(m+j-1,j)*4^(n-m-j)*Sum_{i=0..j} (i-j)^(2*n-2*m)*binomial(2*j,i)*(-1)^(n+j-i) +(-1)^n. - Vladimir Kruchinin, Jun 28 2011
MATHEMATICA
With[{nmax = 60}, CoefficientList[Series[Cos[x/Cos[x]], {x, 0, nmax}], x]*Range[0, nmax]!][[1 ;; -1 ;; 2]] (* G. C. Greubel, Jul 26 2018 *)
PROG
(Maxima)
a(n):=2*sum(binomial(2*n, 2*m)*sum(binomial(m+j-1, j)*4^(n-m-j)*sum((i-j)^(2*n-2*m)*binomial(2*j, i)*(-1)^(n+j-i), i, 0, j), j, 0, n-m), m, 1, n-1)+(-1)^n; /* Vladimir Kruchinin, Jun 28 2011 */
(PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x/cos(x)))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jul 26 2018
CROSSREFS
KEYWORD
sign
AUTHOR
EXTENSIONS
Extended with signs by Olivier Gérard, Mar 15 1997
STATUS
approved