Question 552629
<pre>
There is no common difference, because that is not an arithmetic sequence.
It's also not a geometric sequence, because there is no common ratio.

However the nth term has this formula:

a<sub>n</sub> = -21nē+55n-38.5 

And the sequence taken to a few more terms is:

-4.5,-12.5,-62.5, -154.5, -288.5, -464.5, ...


Edwin</pre>