Sum{T(i,n-i): i=0,1,...,n}, array T as in A047140.

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =12a(5) =20a(6) =40a(7) =80a(8) =160a(9) =320a(10) =578a(11) =1156a(12) =2132a(13) =4264a(14) =8528a(15) =17056a(16) =34112a(17) =64384a(18) =128768a(19) =245292a(20) =490584a(21) =981168a(22) =1962336a(23) =3924672a(24) =7556046a(25) =15112092a(26) =29246744a(27) =58493488a(28) =116986976a(29) =233973952