a(n) = T(2n-1,n-2), T given by A026747.

Terms

a(0) =1a(1) =7a(2) =39a(3) =201a(4) =1000a(5) =4885a(6) =23621a(7) =113543a(8) =543895a(9) =2600204a(10) =12417829a(11) =59278440a(12) =282969385a(13) =1351124510a(14) =6454283276a(15) =30849969965a(16) =147555219782a(17) =706274470775