a(n) = ((1+sqrt(13))^n + (1-sqrt(13))^n)/2.

Terms

a(0) =1a(1) =1a(2) =14a(3) =40a(4) =248a(5) =976a(6) =4928a(7) =21568a(8) =102272a(9) =463360a(10) =2153984a(11) =9868288a(12) =45584384a(13) =209588224a(14) =966189056a(15) =4447436800a(16) =20489142272a(17) =94347526144a(18) =434564759552