# Mathematical induction question

1. Apr 5, 2013

### Googl

Hi all,

I am revising on Proof by mathematical induction and I have came across a question I haven't found a way to work it out.

$$\sum_{r=1}^n r(r!) = (n + 1)! -1$$

I understand the steps of proving by mathematical induction question. The ! is causing the confusion.

2. Apr 5, 2013

### Staff: Mentor

In which way? It is a Factorial.

3. Apr 5, 2013

### Bacle2

Maybe you can rewrite the general summand as:

(r+1)r!-r! and expand the sum, see what happens.