**Do you think we can find a formula that will work for adding all the integers from 1 to n?**

**Think about it! Look over the last three problems we just did -- see anything?**

**Let's write it out the same way:**

**How many pairs of n + 1 are there? Half of n!**

pairs of |

**TEST IT:**

**Find the sum**

**(You know it will be 5050 + 101 = 5151.)**

**Does the formula work?**

**How would you write this series in sigma notation?**