Pearson correlation coefficient

I'm a little confused about this homework problem. Here's the data:

patient------#of current med. problems(x)------post-op length of stay(y)

1---------------------1-------------------------------6

2---------------------2-------------------------------6

3---------------------2------------------------------11

4---------------------1-------------------------------9

5---------------------3------------------------------16

6---------------------1------------------------------16

7---------------------3-------------------------------4

8---------------------5-------------------------------8

9---------------------2------------------------------11

10--------------------3------------------------------13

After caluclating the Pearson correlation coefficient, my final answer came to be -0.085 Here's how I got that number:

[sum]Xi = 23

[sum]Yi=100

[sum]Xi^2=67

[sum]Yi^2=1156

[sum]XiYi=226

n=10

So, when I put those numbers in my formula, I get -40/468.9969

Can you have negative numbers like that? I feel like I did it all right, but that negative 40 makes me think it's wrong.

The other part of the question is to find the least squares regression line. Using all of my numbers, I get 10.92 I think I did that right, but I don't know if the numbers I used to get it were correct. I'm sorry I know this is a long problem, but any help would be great. Thanks!