Constant term in the expansion of (Sum_{k=0..n} k*(x^k + x^(-k)))^3.

Terms

a(0) =0a(1) =0a(2) =12a(3) =84a(4) =324a(5) =924a(6) =2184a(7) =4536a(8) =8568a(9) =15048a(10) =24948a(11) =39468a(12) =60060a(13) =88452a(14) =126672a(15) =177072a(16) =242352a(17) =325584a(18) =430236a(19) =560196a(20) =719796a(21) =913836a(22) =1147608a(23) =1426920a(24) =1758120a(25) =2148120a(26) =2604420a(27) =3135132a(28) =3749004a(29) =4455444