T(2n-1,n-1), T given by A026907.

Terms

a(0) =13a(1) =90a(2) =370a(3) =1403a(4) =5256a(5) =19749a(6) =74628a(7) =283551a(8) =1082440a(9) =4148594a(10) =15953598a(11) =61526960a(12) =237876562a(13) =921678867a(14) =3577968072a(15) =13913243127a(16) =54184698792a(17) =211307360862a(18) =825059443542