a(n) = 4*9^n+1.

Terms

a(0) =5a(1) =37a(2) =325a(3) =2917a(4) =26245a(5) =236197a(6) =2125765a(7) =19131877a(8) =172186885a(9) =1549681957a(10) =13947137605a(11) =125524238437