Fatto matematico: 13771 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 13771 is an unremarkable number.
Data storica: September 13th is the day in 1899 that Mackinder, Ollier and Brocherel make the first ascent of Batian (5,199 m – 17,058 ft), the highest peak of Mount Kenya.