a(n) = 5^n - 4^n.

Terms

a(0) =0a(1) =1a(2) =9a(3) =61a(4) =369a(5) =2101a(6) =11529a(7) =61741a(8) =325089a(9) =1690981a(10) =8717049a(11) =44633821a(12) =227363409a(13) =1153594261a(14) =5835080169a(15) =29443836301a(16) =148292923329a(17) =745759583941