a(n) = (6*11^n - 1)/5.

Terms

a(0) =1a(1) =13a(2) =145a(3) =1597a(4) =17569a(5) =193261a(6) =2125873a(7) =23384605a(8) =257230657a(9) =2829537229a(10) =31124909521a(11) =342374004733