Hecho general: 4123 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Hecho matemático: 4123 is an unremarkable number.
Trivia: 4123 is an uninteresting number.
Fecha histórica: April 15th is the day in 1638 that Tokugawa shogunate forces put down the Shimabara Rebellion when they retake Hara Castle from the rebels.