"Compensation" and "emolument." Article 2, Section 6 states that the president shall receive for his services a "compensation". Later in the section it states that the president shall not receive any other "emolument" from any state.
It cannot change during a president's term.
I believe it's around 9 presidents.
US presidents have a 4-year term.
Four years.
A term
Yes, there is a pension paid to ex-presidents.
An Israeli Presidents' term is 7 years long, and they may only serve one term. Before 1993, a term was 5 years long, and presidents were limited to two terms.
44 presidents but not all of them serve their term
As a group one-term presidents are not so successful which is why they were one-term presidents. Polk refused to run for a second term and he was probably the most successful one-termer. Taft would very probably have won a second term if Theodore Roosevelt had supported him instead of breaking with with his party and running as an independent against him.
The 22nd Amendment.
6