Fatto generale: 9643 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 9643 is the smallest number that can not be formed using the numbers 2^{0}, 2^{1}, ... , 2^{7}, together with the symbols +, –, × and ÷.
Trivia: 9643 is an unremarkable number.
Data storica: May 26th is the day in 1868 that the impeachment trial of U.S. President Andrew Johnson ends with Johnson being found not guilty by one vote.