如题所述
1∙2∙3∙4∙5 = 120 = 5!
1∙2∙3∙4 = 24 = (5-1)! = 4! (5!/5)
1∙2∙3 = 6 = (4-1)! = 3! (4!/4)
1∙2 = 2 = (3-1)! = 2! (3!/3)
1 = (2-1)! = 1! (2!/2)
1!/1 = (1-1)! = 0! = 1/1 = 1
0!/0 = (0-1)! = (-1)! (undefined)
0!/0/-1/-2/⋯/(-n+1) = (0-n)! = (-n)! (undefined)