OFFSET
0,2
COMMENTS
Diagonal of the rational function 1 / (1 - Sum_{k=1..4} x_k + Product_{k=1..4} x_k).
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..418
FORMULA
G.f.: Sum_{k>=0} (4*k)!/k!^4 * x^k / (1+x)^(4*k+1).
MATHEMATICA
a[n_] := Sum[(-1)^(n - k)*(n + 3*k)!/((n - k)!*k!^4), {k, 0, n}]; Array[a, 15, 0] (* Amiram Eldar, Jul 10 2020 *)
PROG
(PARI) {a(n) = sum(k=0, n, (-1)^(n-k)*(n+3*k)!/((n-k)!*k!^4))}
(PARI) N=20; x='x+O('x^N); Vec(sum(k=0, N, (4*k)!/k!^4*x^k/(1+x)^(4*k+1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 10 2020
STATUS
approved