Fatto generale: 4123 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 4123 is a boring number.
Trivia: 4123 is an uninteresting number.
Data storica: April 15th is the day in 1802 that William Wordsworth and his sister, Dorothy see a "long belt" of daffodils, inspiring the former to pen I Wandered Lonely as a Cloud.