OFFSET
0,2
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..535 (terms 0..200 from Seiichi Manyama)
Vaclav Kotesovec, Plot of a(n+1)/a(n) for n = 1..500
MATHEMATICA
Table[Sum[If[a + b + c + d == n, (3 n)!/((n - a)!*(n - b)!*(n - c)!*(n - d)!), 0], {a, 0, n}, {b, 0, a}, {c, 0, b}, {d, 0, c}], {n, 0, 15}] (* Michael De Vlieger, Oct 30 2021 *)
PROG
(PARI) a(n) = sum(a=0, n, sum(b=a, n, sum(c=b, n, sum(d=c, n, if(a+b+c+d==n, (3*n)!/((n-a)!*(n-b)!*(n-c)!*(n-d)!), 0)))));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 30 2021
STATUS
approved