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

Terms

a(0) =1a(1) =12a(2) =50a(3) =133a(4) =279a(5) =506a(6) =832a(7) =1275a(8) =1853a(9) =2584a(10) =3486a(11) =4577a(12) =5875a(13) =7398a(14) =9164a(15) =11191a(16) =13497a(17) =16100a(18) =19018a(19) =22269a(20) =25871a(21) =29842a(22) =34200a(23) =38963a(24) =44149a(25) =49776a(26) =55862a(27) =62425a(28) =69483a(29) =77054