Fatto matematico: 1787 is the number of different arrangements (up to rotation and reflection) of 12 non-attacking queens on a 12×12 chessboard.
Trivia: 1787 is an unremarkable number.
Data storica: November 21st is the day in 1918 that a pogrom takes place in Lwów (now Lviv); over three days, at least 50 Jews and 270 Ukrainian Christians are killed by Poles.