a(n) = ((sqrt(5) + 3)^n + (-sqrt(5) -1)^n + (-sqrt(5) + 3)^n + (sqrt(5) - 1)^n) / 2^n.

Terms

a(0) =4a(1) =2a(2) =10a(3) =14a(4) =54a(5) =112a(6) =340a(7) =814a(8) =2254a(9) =5702a(10) =15250a(11) =39404a(12) =104004a(13) =270922a(14) =711490a(15) =1859134a(16) =4873054a(17) =12748472a(18) =33391060a(19) =87394454a(20) =228841254a(21) =599050102a(22) =1568437210a(23) =4106054164a(24) =10750060804a(25) =28143585362a(26) =73681573690a(27) =192899714414a(28) =505019869254