T(2n-1,n-1), T given by A026568.

Terms

a(0) =1a(1) =2a(2) =8a(3) =34a(4) =121a(5) =606a(6) =2155a(7) =11306a(8) =40717a(9) =217666a(10) =792351a(11) =4280046a(12) =15703156a(13) =85410872a(14) =315180458a(15) =1722900242a(16) =6385672193a(17) =35040356022