John Adams and Thomas Jefferson both died on the same day - 04/07/1826. This was the 50th anniversary of the signing of the American Declaration of Independence, which both men signed. Adams' last words were reported to be "Thomas Jefferson still survives", despite Jefferson having died only a few hours earlier.

Almost every u.s. president to die in office were elected twenty years apart in years ending in zero. These are Harrison (1840), Lincoln (1860), Garfield (1880), McKinley (1900), Harding (1920), FDR (1940) and JFK (1960). Reagan (1980) and Bush (2000) each had assassination attempts on them but both survived to complete their terms. The only exception was Zachery Taylor, who was elected in 1848 and died in 1850.