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

Terms

a(0) =2a(1) =4a(2) =9a(3) =18a(4) =36a(5) =71a(6) =140a(7) =276a(8) =545a(9) =1078a(10) =2136a(11) =4239a(12) =8424a(13) =16760a(14) =33377a(15) =66522a(16) =132668a(17) =264727a(18) =528468a(19) =1055340a(20) =2108097a(21) =4212014a(22) =8417264a(23) =16823583a(24) =33629456a(25) =67230256a(26) =134414145a(27) =268753266a(28) =537385140a(29) =1074573863