a(n) = Sum_{k=0..n} (2^k + Fibonacci(k)).

Terms

a(0) =1a(1) =4a(2) =9a(3) =19a(4) =38a(5) =75a(6) =147a(7) =288a(8) =565a(9) =1111a(10) =2190a(11) =4327a(12) =8567a(13) =16992a(14) =33753a(15) =67131a(16) =133654a(17) =266323a(18) =531051a(19) =1059520a(20) =2114861a(21) =4222959a(22) =8434974a(23) =16852239a(24) =33675823a(25) =67305280a(26) =134535537a(27) =268949683a(28) =537702950a(29) =1075088091