a(n) = (9*n)!/((7*n)!*n!^2).A273629a(n) = (9*n)!/((7*n)!*n!^2).Terms a(0) =1a(1) =72a(2) =18360a(3) =5920200a(4) =2118223800a(5) =803927196072External referencesoeis: A273629