13! (13−4)!4!
13!(13−4)!4!=(134)=134⋅123⋅112⋅101=131⋅1212⋅11⋅102=13⋅1⋅11⋅5=715
13! / (13−4)!4! =6,227,020,800 / [362,880 x 24] =715