Central terms of the triangle in A074911.

Terms

a(0) =1a(1) =4a(2) =20a(3) =108a(4) =632a(5) =4060a(6) =28968a(7) =231000a(8) =2058096a(9) =20375964a(10) =222393800a(11) =2653879624a(12) =34365597840a(13) =479776469848