a(n) = (9*n^2 - n)/2 + 1.

Terms

a(0) =1a(1) =5a(2) =18a(3) =40a(4) =71a(5) =111a(6) =160a(7) =218a(8) =285a(9) =361a(10) =446a(11) =540a(12) =643a(13) =755a(14) =876a(15) =1006a(16) =1145a(17) =1293a(18) =1450a(19) =1616a(20) =1791a(21) =1975a(22) =2168a(23) =2370a(24) =2581a(25) =2801a(26) =3030a(27) =3268a(28) =3515a(29) =3771