a(n) = (-2 - (-1)^n*(-2 + n) + n + 2*n^3)/4.

Terms

a(0) =0a(1) =0a(2) =4a(3) =14a(4) =32a(5) =64a(6) =108a(7) =174a(8) =256a(9) =368a(10) =500a(11) =670a(12) =864a(13) =1104a(14) =1372a(15) =1694a(16) =2048a(17) =2464a(18) =2916a(19) =3438a(20) =4000a(21) =4640a(22) =5324a(23) =6094a(24) =6912a(25) =7824a(26) =8788a(27) =9854a(28) =10976a(29) =12208