Fatto generale: 2491 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 2491 is the product of two consecutive primes.
Trivia: 2491 is a boring number.
Data storica: October 26th is the day in 1999 that Britain's House of Lords votes to end the right of hereditary peers to vote in Britain's upper chamber of Parliament.