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

Terms

a(0) =1a(1) =3a(2) =10a(3) =30a(4) =84a(5) =227a(6) =603a(7) =1589a(8) =4172a(9) =10936a(10) =28646a(11) =75013a(12) =196405a(13) =514215a(14) =1346254a(15) =3524562a(16) =9227448a(17) =24157799a(18) =63245967a(19) =165580121a(20) =433494416a(21) =1134903148a(22) =2971215050a(23) =7778742025a(24) =20365011049a(25) =53316291147a(26) =139583862418