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

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =73a(5) =201a(6) =546a(7) =1469a(8) =3925a(9) =10434a(10) =27633a(11) =72977a(12) =192322a(13) =506037a(14) =1329885a(15) =3491810a(16) =9161929a(17) =24026745a(18) =62983842a(19) =165055853a(20) =432445861a(21) =1132806018a(22) =2967020769a(23) =7770353441a(24) =20348233858a(25) =53282736741a(26) =139516753581a(27) =365301078434a(28) =956453590585