Even Fibonacci numbers; or, Fibonacci(3*n).

Terms

a(0) =0a(1) =2a(2) =8a(3) =34a(4) =144a(5) =610a(6) =2584a(7) =10946a(8) =46368a(9) =196418a(10) =832040a(11) =3524578a(12) =14930352a(13) =63245986a(14) =267914296a(15) =1134903170a(16) =4807526976a(17) =20365011074a(18) =86267571272a(19) =365435296162