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

Terms

a(0) =1a(1) =9a(2) =58a(3) =329a(4) =1753a(5) =9020a(6) =45442a(7) =225860a(8) =1112543a(9) =5446607a(10) =26550968a(11) =129042976a(12) =625860205a(13) =3031021096a(14) =14664729519a(15) =70906318405a(16) =342717456708