a(n) = (1/2)*A026907(2*n, n).

Terms

a(0) =22a(1) =99a(2) =379a(3) =1412a(4) =5265a(5) =19758a(6) =74637a(7) =283560a(8) =1082449a(9) =4148603a(10) =15953607a(11) =61526969a(12) =237876571a(13) =921678876a(14) =3577968081a(15) =13913243136a(16) =54184698801a(17) =211307360871a(18) =825059443551