a(n) = 4*(n + 1)*(n + 2)*(4*n + 3)/3.

Terms

a(0) =8a(1) =56a(2) =176a(3) =400a(4) =760a(5) =1288a(6) =2016a(7) =2976a(8) =4200a(9) =5720a(10) =7568a(11) =9776a(12) =12376a(13) =15400a(14) =18880a(15) =22848a(16) =27336a(17) =32376a(18) =38000a(19) =44240a(20) =51128a(21) =58696a(22) =66976a(23) =76000a(24) =85800a(25) =96408a(26) =107856a(27) =120176a(28) =133400a(29) =147560