a(n) = (1/12)*n^2*(3*(1 + n^2) - 2*(2 + n^2)*(n mod 2)).

Terms

a(0) =0a(1) =0a(2) =5a(3) =6a(4) =68a(5) =50a(6) =333a(7) =196a(8) =1040a(9) =540a(10) =2525a(11) =1210a(12) =5220a(13) =2366a(14) =9653a(15) =4200a(16) =16448a(17) =6936a(18) =26325a(19) =10830a(20) =40100a(21) =16170a(22) =58685a(23) =23276a(24) =83088a(25) =32500a(26) =114413a(27) =44226a(28) =153860a(29) =58870