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

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =4a(5) =8a(6) =12a(7) =21a(8) =33a(9) =55a(10) =88a(11) =144a(12) =232a(13) =377a(14) =609a(15) =987a(16) =1596a(17) =2584a(18) =4180a(19) =6765a(20) =10945a(21) =17711a(22) =28656a(23) =46368a(24) =75024a(25) =121393a(26) =196417a(27) =317811a(28) =514228a(29) =832040