Fatto matematico: 8404 is the number of connected graphs with 9 vertices and 13 edges.
Trivia: 8404 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: January 3rd is the day in 1997 that China announces it will spend US$27.7 billion to fight erosion and pollution in the Yangtze and Yellow River valleys.