1, $(n!)^{2}>n^{n}$ ( Với $n\in Z^{+},n>2$)2, $1+\frac{1}{1!}+\frac{1}{2!}+\frac{1}{3!}+...+\frac{1}{n!}<3$3, $C^{1}_{n}+2\frac{C^{2}_{n}}{C^{1}_{n}}+3\frac{C^{3}_{n}}{C^{2}_{n}}+...+k\frac{C^{k}_{n}}{C^{k-1}_{n}}+...+n\frac{C^{n}_{n}}{C^{n-1}_{n}}=\frac{n(n+1)}{2}$