a(n) = ((4+sqrt(5))*(2+sqrt(5))^n + (4-sqrt(5))*(2-sqrt(5))^n)/2.

A163070

a(n) = ((4+sqrt(5))*(2+sqrt(5))^n + (4-sqrt(5))*(2-sqrt(5))^n)/2.

Terms

    a(0) =4a(1) =13a(2) =56a(3) =237a(4) =1004a(5) =4253a(6) =18016a(7) =76317a(8) =323284a(9) =1369453a(10) =5801096a(11) =24573837a(12) =104096444a(13) =440959613a(14) =1867934896a(15) =7912699197a(16) =33518731684a(17) =141987625933a(18) =601469235416

External references