(1/2)*Sum{T(n,i): i=0,1,...,n}, where T is given by A048113.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =6a(5) =12a(6) =24a(7) =42a(8) =84a(9) =168a(10) =312a(11) =624a(12) =1248a(13) =2388a(14) =4776a(15) =9552a(16) =18576a(17) =37152a(18) =74304a(19) =145884a(20) =291768a(21) =583536a(22) =1152456a(23) =2304912a(24) =4609824a(25) =9138888a(26) =18277776a(27) =36555552a(28) =72654552a(29) =145309104