a(n) = 5*n^2/2 - 5*n + 13/4 - (-1)^n/4.

Terms

a(0) =1a(1) =3a(2) =11a(3) =23a(4) =41a(5) =63a(6) =91a(7) =123a(8) =161a(9) =203a(10) =251a(11) =303a(12) =361a(13) =423a(14) =491a(15) =563a(16) =641a(17) =723a(18) =811a(19) =903a(20) =1001a(21) =1103a(22) =1211a(23) =1323a(24) =1441a(25) =1563a(26) =1691a(27) =1823a(28) =1961a(29) =2103