Fatto matematico: 4251 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 4251 is an uninteresting number.
Data storica: August 21st is the day in 1879 that the Virgin Mary, along with St. Joseph and St. John the Evangelist, reportedly appears at Knock Shrine in Knock, County Mayo, Ireland.