a(n) = trinomial(2*n, 4) = (1/6)*n*(2*n - 1)*(2*n^2 + 7*n - 3).

Terms

a(0) =0a(1) =1a(2) =19a(3) =90a(4) =266a(5) =615a(6) =1221a(7) =2184a(8) =3620a(9) =5661a(10) =8455a(11) =12166a(12) =16974a(13) =23075a(14) =30681a(15) =40020a(16) =51336a(17) =64889a(18) =80955a(19) =99826a(20) =121810a(21) =147231a(22) =176429a(23) =209760a(24) =247596a(25) =290325a(26) =338351a(27) =392094a(28) =451990a(29) =518491