a(n) = (4*n^3 - 6*n^2 + 8*n + 9 + 3*(-1)^n)/12.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =17a(5) =33a(6) =59a(7) =95a(8) =145a(9) =209a(10) =291a(11) =391a(12) =513a(13) =657a(14) =827a(15) =1023a(16) =1249a(17) =1505a(18) =1795a(19) =2119a(20) =2481a(21) =2881a(22) =3323a(23) =3807a(24) =4337a(25) =4913a(26) =5539a(27) =6215a(28) =6945a(29) =7729