There is at least one more famous mathematician: Isaac Newton. But that proves your point. How many average people could identify anyone else, even Euclid?
I guess most who do know him as a mathematician also know Leibniz.
As a mathematician, Pythagoras probably is way better known than Newton.
Also, it strongly depends on where in the world you ask, many Londoners will have heard of Christopher Wren for instance. And loads of people know of classical mathematicians such as Archimedes and Da Vinci. Also you get the crossovers such as people like Ada Lovelace, who will be known to many fans of Byron.
You probably need to take a survey.