a(n) = T(2n-1,n-2), T given by A026758.

Terms

a(0) =1a(1) =7a(2) =38a(3) =190a(4) =918a(5) =4365a(6) =20594a(7) =96804a(8) =454362a(9) =2132121a(10) =10010203a(11) =47042042a(12) =221337726a(13) =1042837195a(14) =4920447410a(15) =23250646651a(16) =110029743083a(17) =521462857972