a(n) = Fibonacci(3n) - Fibonacci(2n).

Terms

a(0) =0a(1) =1a(2) =5a(3) =26a(4) =123a(5) =555a(6) =2440a(7) =10569a(8) =45381a(9) =193834a(10) =825275a(11) =3506867a(12) =14883984a(13) =63124593a(14) =267596485a(15) =1134071130a(16) =4805348667a(17) =20359308187a(18) =86252640920a(19) =365396207993