a(n) = A142585(n) + A142586(n).

Terms

a(0) =2a(1) =2a(2) =6a(3) =14a(4) =38a(5) =112a(6) =276a(7) =814a(8) =1998a(9) =5702a(10) =14226a(11) =39404a(12) =99908a(13) =270922a(14) =695106a(15) =1859134a(16) =4807518a(17) =12748472a(18) =33128916a(19) =87394454a(20) =227792678a(21) =599050102a(22) =1564242906a(23) =4106054164a(24) =10733283588a(25) =28143585362a(26) =73614464826a(27) =192899714414a(28) =504751433798