When a plane crashes, what do they do with the flight number?

Factual Questions
1

I’ve been wondering this. For example, say flight 635 crashes. Will they ever use the number “635” for a flight again? If not, why not? Most people wouldn’t mind being on a flight with the same number as a previously crashed flight (I’m sure those who even knew the flight number that crashed, and made the connection would be smart enough to understand that it’s just a coincidence.), unless it was a paticularly famous crash (i.e. TWA 800, UA 93, etc).

So, what do they do with the numbers of doomed flights?

2

The airline retires the number.
For example, American 11 is now American 25.

3

Well, for at least one air crash off of the California coast (The one off of Point Magu), the company kept the number for at least a short time afterwards.