Sum{T(i,n-i): i=0,1,...,n}, array T as in A047089.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =12a(5) =21a(6) =42a(7) =84a(8) =155a(9) =310a(10) =620a(11) =1176a(12) =2352a(13) =4704a(14) =9071a(15) =18142a(16) =36284a(17) =70717a(18) =141434a(19) =282868a(20) =555268a(21) =1110536a(22) =2221072a(23) =4381656a(24) =8763312a(25) =17526624a(26) =34697879a(27) =69395758a(28) =138791516a(29) =275467455