a(n) = (4*n^3 + 6*n^2 + 8*n + 6)/3.

Terms

a(0) =2a(1) =8a(2) =26a(3) =64a(4) =130a(5) =232a(6) =378a(7) =576a(8) =834a(9) =1160a(10) =1562a(11) =2048a(12) =2626a(13) =3304a(14) =4090a(15) =4992a(16) =6018a(17) =7176a(18) =8474a(19) =9920a(20) =11522a(21) =13288a(22) =15226a(23) =17344a(24) =19650a(25) =22152a(26) =24858a(27) =27776a(28) =30914a(29) =34280