a(n) = n!*(n+1)!/2.A010796a(n) = n!*(n+1)!/2.Terms a(0) =1a(1) =6a(2) =72a(3) =1440a(4) =43200a(5) =1814400a(6) =101606400a(7) =7315660800a(8) =658409472000External referencesoeis: A010796