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

Terms

a(0) =1a(1) =2a(2) =6a(3) =17a(4) =46a(5) =122a(6) =321a(7) =842a(8) =2206a(9) =5777a(10) =15126a(11) =39602a(12) =103681a(13) =271442a(14) =710646a(15) =1860497a(16) =4870846a(17) =12752042a(18) =33385281a(19) =87403802a(20) =228826126a(21) =599074577a(22) =1568397606a(23) =4106118242a(24) =10749957121a(25) =28143753122a(26) =73681302246a(27) =192900153617a(28) =505019158606