a(n) = 5^n-4^n+1.

Terms

a(0) =1a(1) =2a(2) =10a(3) =62a(4) =370a(5) =2102a(6) =11530a(7) =61742a(8) =325090a(9) =1690982a(10) =8717050a(11) =44633822a(12) =227363410a(13) =1153594262a(14) =5835080170a(15) =29443836302a(16) =148292923330a(17) =745759583942