a(1)=0; for n>1, a(n) = 4*n^3 - 3*n^2 - 3*n + 4.

Terms

a(0) =0a(1) =18a(2) =76a(3) =200a(4) =414a(5) =742a(6) =1208a(7) =1836a(8) =2650a(9) =3674a(10) =4932a(11) =6448a(12) =8246a(13) =10350a(14) =12784a(15) =15572a(16) =18738a(17) =22306a(18) =26300a(19) =30744a(20) =35662a(21) =41078a(22) =47016a(23) =53500a(24) =60554a(25) =68202a(26) =76468a(27) =85376a(28) =94950a(29) =105214