Hecho general: 4005 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Hecho matemático: 4005 is a triangular number whose internal digits are triangular and whose external digits are triangular.
Trivia: 4005 is a boring number.
Fecha histórica: December 18th is the day in 1888 that Richard Wetherill and his brother in-law discover the ancient Indian ruins of Cliff Palace in Mesa Verde.