Fatto generale: 406 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 406 is the number of ways to tile a 3×17 rectangle with 3×1 rectangles.
Trivia: 406 is an unremarkable number.
Data storica: February 9th is the day in 1959 that the R-7 Semyorka, the first intercontinental ballistic missile, becomes operational at Plesetsk, USSR.