Hecho general: 691 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Hecho matemático: 691 is the smallest prime p for which x^{5} = x^{4} + x^{3} + x^{2} + x + 1 (mod p) has 5 solutions.
Trivia: 691 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fecha histórica: November 21st is the day in 1918 that Flag of Estonia, previously used by pro-independence activists, is formally adopted as national flag of the Republic of Estonia.