a(n) = 3*11^n+1.

Terms

a(0) =4a(1) =34a(2) =364a(3) =3994a(4) =43924a(5) =483154a(6) =5314684a(7) =58461514a(8) =643076644a(9) =7073843074a(10) =77812273804a(11) =855935011834