a(n) = n*(27*n - 1)/2.

Terms

a(0) =0a(1) =13a(2) =53a(3) =120a(4) =214a(5) =335a(6) =483a(7) =658a(8) =860a(9) =1089a(10) =1345a(11) =1628a(12) =1938a(13) =2275a(14) =2639a(15) =3030a(16) =3448a(17) =3893a(18) =4365a(19) =4864a(20) =5390a(21) =5943a(22) =6523a(23) =7130a(24) =7764a(25) =8425a(26) =9113a(27) =9828a(28) =10570a(29) =11339