Only Living President

As of this writing, there is one sitting president and 5 ex-presidents: President Biden, Donald Trump, Barack Obama, George W. Bush, Bill Clinton, and Jimmy Carter.  There have never been more than 5 living ex-presidents.  One supposes that after George Washington, the following presidents always had a predecessor enjoying his retirement.  In fact, no.  Several presidents have been the only living president during their presidency.

George Washington (1789-1797): As the first president, Washington had no predecessors to consult in the difficult times.  It was up to him to establish how Article 2 of the Constitution would work.  For nearly 8 years, he was the only living president.

John Adams (1797-1801): Having been Washington's VP, Adams knew his predecessor fairly well.  He even called upon Washington to lead an army during the Whiskey Rebellion.  However, Washington died in December 1799, leaving John Adams as the only living president.  He did not win re-election the following year, so his tenure as the only living president was only 1 year and 4 months.

Ulysses S. Grant (1869-1877): When Grant began his presidency in March 1869, there were 3 ex-presidents: Millard Filmore, Franklin Pierce, and Andrew Johnson.  Pierce died in October 1869, Filmore in January 1874, and Johnson on July 31, 1875.  For the next year and 8 months, Grant was the only living president.

Theodore Roosevelt (1901-1909): Theodore took office upon the assassination of McKinley.  At that time, only 1 previous president was still living: Grover Cleveland.  When Cleveland died on June 24, 1908, Roosevelt was the only living president.  Eight months later, Roosevelt left office.

Herbert Hoover (1929-1933): When Hoover came to office, former President Taft was the Chief Justice of the Supreme Court and Calvin Coolidge retired to Massachusetts.  Taft died in 1930 and Coolidge died on January 5, 1933.  Hoover was the only living president for 2 months.

Richard Nixon (1969-1974): Nixon took office when there were 3 living former presidents.  Harry Truman, Dwight Eisenhower, and Lyndon B. Johnson.  Eisenhower died a couple of months after Nixon was inaugurated in 1969.  Truman died in December 1972 and Johnson died a month later, January 22, 1973.  Richard Nixon was the only living president for the next 18 months, at which time he resigned.

Since 1981, there have been 3 to 5 living former presidents.