1 < (1!+2!+3!+4!+5!+...+n!)/n!< (1!+2!+...(n-2)!+(n-1)!+n!)/n!
< [(n-2)!(n-2)+(n-1)!+n!]/n!< 1/n + 1/n + 1
∴ lim(n->∞) (1/n + 1/n + 1 ) = 1 ,由夹逼定理:
lim(n->∞) (1!+2!+3!+4!+5!+...+n!)/n!= 1
1 < (1!+2!+3!+4!+5!+...+n!)/n!< (1!+2!+...(n-2)!+(n-1)!+n!)/n!
< [(n-2)!(n-2)+(n-1)!+n!]/n!< 1/n + 1/n + 1
∴ lim(n->∞) (1/n + 1/n + 1 ) = 1 ,由夹逼定理:
lim(n->∞) (1!+2!+3!+4!+5!+...+n!)/n!= 1