eight because of the death of a president. These eight so-called 'accidental presidents' were John Tyler (VP for W, H. Harrison) Millard Fillmore (VP for Taylor) Andrew Johnson (VP for Lincoln), Chester A. Arthur (VP for Garfield), Theodore Roosevelt(VP for McKinley), Calvin Coolidge (VP for Harding), Harry S. Truman (VP for F.D. Roosevelt), and Lyndon B. Johnson (VP for Kennedy). Vice-president Gerald Ford (VP for Nixon) took office because of President Nixon's resignation. The other vice presidents who became president were John Adams (VP for Washington), Thomas Jefferson, (VP for John Adams), Martin Van Buren (VP for Jackson), Richard M. Nixon (VP for Eisenhower) and George H. W. Bush (VP for Reagan). Of these six, all but Nixon were elected president immediately after serving as vice president. Nixon was defeated in 1960 but ran again and won in 1968.
Source here.
