a(n) = A192457(n)/2.

Terms

a(0) =0a(1) =1a(2) =7a(3) =59a(4) =605a(5) =7365a(6) =104055a(7) =1675275a(8) =30290085a(9) =607828725a(10) =13406691375a(11) =322415322075