When looking for your number of ancestors one has to keep in mind that every time someone mates with a cousin no matter how far removed is would cut the number of ancestors in the preceding generation for the progeny by half.
Since within a few hundred years back the chances of mating with a cousin of some sort improve considerably it makes it kind of hard to figure.
You are very likely to have some people ancestral to you on both sides.
How would you count them? In 10 (American Revolution) generations you will have 2048 ancestors. In 20-- 2,097,152. A million males and a million females.
There is a pretty good chance that any one of one group "knew" any one of the other :wink:
It works like this in epidemicology also. In the 70s there were numerous articles on how the AIDS epidemic would infect us all by 2005. Didn't happen