I want to figure out the proper summation to figure out a sum of products:

5

x3

----

15

x3

----

45

x3

----

135

x3

___

...

So if n=0 the result is 5, if n=1 the result is 5+15, if n=2, the result is 5+15+45 and so. Hopefully that makes sense. I'm not quite sure how else to put it. Would the best way be to do something like ? Or is there some more concise way of putting it? I appreciate any help you guys can offer. Thanks.