Franklin D. Roosevelt was the only President to serve into a fourth term.
I believe it's around 9 presidents.
44 presidents but not all of them serve their term
20
six
all of them
Two
5 of the first 10 presidents were re-elected for a second term.
3
3
4 years
It cannot change during a president's term.
I am not quite sure what " went for" means to you. Only two presidents announced early in their administration that they would not seek a second term and they were James Polk and Rutherford Hayes.