a(n) = (n-3)*(n-2)*(n-1)*n*(n+1)/30.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =4a(5) =24a(6) =84a(7) =224a(8) =504a(9) =1008a(10) =1848a(11) =3168a(12) =5148a(13) =8008a(14) =12012a(15) =17472a(16) =24752a(17) =34272a(18) =46512a(19) =62016a(20) =81396a(21) =105336a(22) =134596a(23) =170016a(24) =212520a(25) =263120a(26) =322920a(27) =393120a(28) =475020a(29) =570024