In The Shining, room 217 is the room that is focused on as having a dark history and being a haunted room due to the tragedy of Mrs. Massey. Danny is warned not to enter this room and anyone who enters the room has bizarre encounters.
Why did Stephen King choose the room number 217 for his novel? What is the significance of this room number to him?
George Beahm writes in his books about Stephen King that the family was in fact in a Room 217 when the idea came to him.
Stephen King from A to Z says:
The genesis of [The Shining] is that when the Kings were in Boulder, they wanted to get away for a weekend. Locals recommended the Stanley Hotel in Estes Park.
The Kings arrived at the Stanley Hotel on October 30, 1974, just as it was closing down for the winter, but the manager let the Kings stay.
And then, for the rest of the story, we go to Stephen King: America’s Best-Loved Boogeyman:
When King left, he got lost in the maze of corridors, then found his way to room 217, where he went to the bathroom, pulled back the pink curtain drawn across the bathtub, and noticed the clawfoot porcelain tub. "What if somebody died here? At that moment, I knew that I had a book.”
It seems apocryphal, but the references are authoritative enough that it's likely true.
Stephen King applies the number 19 in many many novels. Sometimes it’s a variation, sometimes it’s adding numbers together to get to 19, like the numbers in a date in his books or in this case, 2+17. He goes into detail about it in the Dark Tower books, that the number 19 is significant in the Stephen King universe- and indeed, it pops up all over. In Stephen King’s book End of Watch, Brady Hartsfield, the powerful antagonist, is in a vegetative state in hospital room 217. It’s fun to come across these little hidden Easter eggs.
