Third column of triangle in A234950.

Terms

a(0) =2a(1) =20a(2) =135a(3) =770a(4) =4004a(5) =19656a(6) =92820a(7) =426360a(8) =1918620a(9) =8498776a(10) =37182145a(11) =161056350a(12) =691945800a(13) =2952675600a(14) =12527780760a(15) =52895074320a(16) =222399744300a(17) =931689977400