# proof

• May 6th 2012, 04:55 AM
Mhmh96
proof
• May 6th 2012, 07:45 AM
Plato
Re: proof
Quote:

Originally Posted by Mhmh96

Note that $\sum\limits_{k = 1}^5 {k!} = 153$ is a multiple of nine.

Also, if $N\ge 6$ then $6!={\color{blue}6}\cdot 5\cdot 4\cdot{\color{blue}3}\cdot 2={\color{blue}720}$ which is a multiple of nine.

If $N\ge 6$ then $N!$ is a multiple of nine. WHY?