Still I need 8 great grandparents discounting everyone else. 20 generations ago I, myself had to of had 1,048,576 grandparents whether they were shared by many others or not. A biological fact, right?
no, fellah. read again.
your family tree crosses itself many times.
meaning that some of your ancestors are represented as "20th-great grandfather" through multiple lines, essentially creating "virtual" duplication where no real duplication has occured.
shall I generate a chart to graphically explain this process?