Fatto generale: 16557 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 16557 is an unremarkable number.
Trivia: 16557 is a boring number.
Data storica: April 30th is the day in 1927 that the Federal Industrial Institute for Women opens in Alderson, West Virginia, as the first women's federal prison in the United States.