a(n) = 36*n^2 - 6.

Terms

a(0) =30a(1) =138a(2) =318a(3) =570a(4) =894a(5) =1290a(6) =1758a(7) =2298a(8) =2910a(9) =3594a(10) =4350a(11) =5178a(12) =6078a(13) =7050a(14) =8094a(15) =9210a(16) =10398a(17) =11658a(18) =12990a(19) =14394a(20) =15870a(21) =17418a(22) =19038a(23) =20730a(24) =22494a(25) =24330a(26) =26238a(27) =28218a(28) =30270a(29) =32394