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

Terms

a(0) =1a(1) =4a(2) =73a(3) =730a(4) =5185a(5) =30376a(6) =157465a(7) =750142a(8) =3359233a(9) =14348908a(10) =59049001a(11) =235782658a(12) =918330049a(13) =3502727632a(14) =13124466937a(15) =48427561126a(16) =176319369217a(17) =634465620820