Fatto generale: 1381 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1381 is the number of anisohedral 17-ominoes.
Trivia: 1381 is an uninteresting number.
Data storica: October 12th is the day in 1398 that the Treaty of Salynas is signed between Grand Duke of Lithuania Vytautas the Great and the Teutonic Knights, who received Samogitia.