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

Terms

a(0) =2a(1) =14a(2) =35a(3) =65a(4) =104a(5) =152a(6) =209a(7) =275a(8) =350a(9) =434a(10) =527a(11) =629a(12) =740a(13) =860a(14) =989a(15) =1127a(16) =1274a(17) =1430a(18) =1595a(19) =1769a(20) =1952a(21) =2144a(22) =2345a(23) =2555a(24) =2774a(25) =3002a(26) =3239a(27) =3485a(28) =3740a(29) =4004