T(2n-1,n-2), T given by A026681.

Terms

a(0) =1a(1) =9a(2) =37a(3) =237a(4) =913a(5) =5506a(6) =21113a(7) =124845a(8) =480515a(9) =2818051a(10) =10898715a(11) =63665402a(12) =247327912a(13) =1441838546a(14) =5623080622a(15) =32744927553a(16) =128128256975a(17) =745693719711