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

Terms

a(0) =0a(1) =-1a(2) =3a(3) =4a(4) =21a(5) =45a(6) =144a(7) =351a(8) =987a(9) =2516a(10) =6765a(11) =17533a(12) =46368a(13) =120927a(14) =317811a(15) =830820a(16) =2178309a(17) =5699693a(18) =14930352a(19) =39079807a(20) =102334155a(21) =267892404a(22) =701408733a(23) =1836254589a(24) =4807526976a(25) =12586118975a(26) =32951280099a(27) =86267178436a(28) =225851433717a(29) =591285701421