a(n) = Fibonacci(4*n+3).

Terms

a(0) =2a(1) =13a(2) =89a(3) =610a(4) =4181a(5) =28657a(6) =196418a(7) =1346269a(8) =9227465a(9) =63245986a(10) =433494437a(11) =2971215073a(12) =20365011074a(13) =139583862445a(14) =956722026041