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

Terms

a(0) =1a(1) =40a(2) =196a(3) =550a(4) =1183a(5) =2176a(6) =3610a(7) =5566a(8) =8125a(9) =11368a(10) =15376a(11) =20230a(12) =26011a(13) =32800a(14) =40678a(15) =49726a(16) =60025a(17) =71656a(18) =84700a(19) =99238a(20) =115351a(21) =133120a(22) =152626a(23) =173950a(24) =197173a(25) =222376a(26) =249640a(27) =279046a(28) =310675a(29) =344608