a(n) = 1 - 5*(n + 1)^2 + 5*(n + 1)^4.

Terms

a(0) =1a(1) =61a(2) =361a(3) =1201a(4) =3001a(5) =6301a(6) =11761a(7) =20161a(8) =32401a(9) =49501a(10) =72601a(11) =102961a(12) =141961a(13) =191101a(14) =252001a(15) =326401a(16) =416161a(17) =523261a(18) =649801a(19) =798001a(20) =970201a(21) =1168861a(22) =1396561a(23) =1656001a(24) =1950001a(25) =2281501a(26) =2653561a(27) =3069361a(28) =3532201a(29) =4045501