Fatto generale: 20503 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 20503 is an unremarkable number.
Trivia: 20503 is an uninteresting number.
Data storica: February 18th is the day in 1745 that the city of Surakarta, Central Java is founded on the banks of Bengawan Solo River, and becomes the capital of the Kingdom of Surakarta.