From https://en.wikipedia.org/wiki/400_(number)#406 :

• 406 = 2 × 7 × 29
• sphenic number,
• triangular number,
• centered nonagonal number,
• nontotient

Also:

• HTTP status code for "Not Acceptable".
• Wikisource has original text related to this article:

406 is a poem by John Boyle O'Reilly. It was believed to have been the number of one of O'Reilly's prison cells, and was the number of his first hotel room after he arrived in the United States. Hence the number had a mystical significance to him, as intimated in the poem.

• Peugeot 406 car.
• Area code for all of Montana.

Here’s Q Drop #406: https://qalerts.app/?q=%23406

u/#q406

See you tomorrow, Frens!🤓