Fatto generale: 4121 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 4121 is a number whose product of digits is equal to its sum of digits.
Trivia: 4121 is an unremarkable number.
Data storica: April 13th is the day in 1943 that the Jefferson Memorial is dedicated in Washington, D.C., on the 200th anniversary of Thomas Jefferson's birth.