+870 It's because $$(n-1)!=\frac{n!}{n}$$
That means :
$$\\6!=1\times 2\times 3\times 4\times 5\times 6=720
\\(6-1)!=5!=\frac{6!}{6}=120
\\(5-1)!=4!=\frac{5!}{5}=24
\\(4-1)!=3!=\frac{4!}{4}=6
\\(3-1)!=2!=\frac{3!}{3}=2
\\(2-1)!=1!=\frac{2!}{2}=1
\\\textcolor[rgb]{0,0,1}{(1-1)!=0!=\frac{1!}{1}=1}$$
+870 It's because $$(n-1)!=\frac{n!}{n}$$
That means :
$$\\6!=1\times 2\times 3\times 4\times 5\times 6=720
\\(6-1)!=5!=\frac{6!}{6}=120
\\(5-1)!=4!=\frac{5!}{5}=24
\\(4-1)!=3!=\frac{4!}{4}=6
\\(3-1)!=2!=\frac{3!}{3}=2
\\(2-1)!=1!=\frac{2!}{2}=1
\\\textcolor[rgb]{0,0,1}{(1-1)!=0!=\frac{1!}{1}=1}$$
