a(n) = 3*n*(6*n + 1).

Terms

a(0) =0a(1) =21a(2) =78a(3) =171a(4) =300a(5) =465a(6) =666a(7) =903a(8) =1176a(9) =1485a(10) =1830a(11) =2211a(12) =2628a(13) =3081a(14) =3570a(15) =4095a(16) =4656a(17) =5253a(18) =5886a(19) =6555a(20) =7260a(21) =8001a(22) =8778a(23) =9591a(24) =10440a(25) =11325a(26) =12246a(27) =13203a(28) =14196a(29) =15225