Question 1164945
<pre>
Simplest pattern is:

Start with 3:
 
We have  3, subtract 9, get -6.
We have -6, add twice 9, get 12.
We have 12, subtract 8, get 4.
We have  4, add twice 8, get 20.
We have 20, subtract 7, get 13.
We have 13, add twice 7, get 27.
We have 27, subtract 6, get 21.
We have  21, add twice 6, get 33.
We have 33, subtract 5, get 28.
We have  28, add twice 5, get 38.
...

Edwin</pre>