a(n) = T(2n-1,n-2), T given by A026648.

Terms

a(0) =1a(1) =7a(2) =30a(3) =148a(4) =610a(5) =2823a(6) =11690a(7) =52952a(8) =221094a(9) =992190a(10) =4173708a(11) =18642456a(12) =78906516a(13) =351537963a(14) =1495497690a(15) =6652572976a(16) =28420125190a(17) =126308309058a(18) =541492971140