a(n) = T(2n-1, n-2), T given by A026780.

Terms

a(0) =1a(1) =9a(2) =60a(3) =361a(4) =2076a(5) =11672a(6) =64842a(7) =357897a(8) =1968788a(9) =10813804a(10) =59372770a(11) =326086492a(12) =1792293014a(13) =9861375614a(14) =54324086446a(15) =299651439321