a(n) = (2*n - 1)*(8*n^2 - 8*n + 3)/3.

Terms

a(0) =1a(1) =19a(2) =85a(3) =231a(4) =489a(5) =891a(6) =1469a(7) =2255a(8) =3281a(9) =4579a(10) =6181a(11) =8119a(12) =10425a(13) =13131a(14) =16269a(15) =19871a(16) =23969a(17) =28595a(18) =33781a(19) =39559a(20) =45961a(21) =53019a(22) =60765a(23) =69231a(24) =78449a(25) =88451a(26) =99269a(27) =110935a(28) =123481a(29) =136939