Sum{T(i,n-i): i=0,1,...,n}, array T as in A047120.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =9a(5) =18a(6) =36a(7) =69a(8) =134a(9) =263a(10) =526a(11) =1052a(12) =2085a(13) =4143a(14) =8250a(15) =16500a(16) =33000a(17) =65851a(18) =131484a(19) =262668a(20) =525336a(21) =1050672a(22) =2100045a(23) =4198157a(24) =8393603a(25) =16787206a(26) =33574412a(27) =67136750a(28) =134255332a(29) =268484858