a(n) = Fibonacci(3*n) - (2 + (-1)^n)*Fibonacci(n).

Terms

a(0) =1a(1) =5a(2) =32a(3) =135a(4) =605a(5) =2560a(6) =10933a(7) =46305a(8) =196384a(9) =831875a(10) =3524489a(11) =14929920a(12) =63245753a(13) =267913165a(14) =1134902560a(15) =4807524015a(16) =20365009477a(17) =86267563520a(18) =365435291981