a(n) = a(n-1) + 20*a(n-2), n >= 2; a(0)=1, a(1)=41.

Terms

a(0) =1a(1) =41a(2) =61a(3) =881a(4) =2101a(5) =19721a(6) =61741a(7) =456161a(8) =1690981a(9) =10814201a(10) =44633821a(11) =260917841a(12) =1153594261a(13) =6371951081a(14) =29443836301a(15) =156882857921a(16) =745759583941