a(n) = if n mod 2 = 1 then (n^2-1)*n^3/4 else n^5/4.

Terms

a(0) =0a(1) =0a(2) =8a(3) =54a(4) =256a(5) =750a(6) =1944a(7) =4116a(8) =8192a(9) =14580a(10) =25000a(11) =39930a(12) =62208a(13) =92274a(14) =134456a(15) =189000a(16) =262144a(17) =353736a(18) =472392a(19) =617310a(20) =800000a(21) =1018710a(22) =1288408a(23) =1606044a(24) =1990656a(25) =2437500a(26) =2970344a(27) =3582306a(28) =4302592a(29) =5121690