Mine a vanity prefix for your Nostr npub

download glasnostr here: github/glasnostr
Unpack it: tar -xvf {archive-filename}.tar.gz
Give it execution permissions: chmod +x glasnostr
Run it: ./glasnostr f00

The character set for a valid npub is 023456789acdefghjklmnpqrstuvwxyz so only mine prefixes with these characters.

Here are some rough estimates for a modern laptop or mobile phone:
1 character = usually less than 0.1 seconds
2 characters = usually less than a second
3 characters = usually less than 30 seconds
4 characters = usually less than 10 minutes
5 characters = usually less than 1 hour
6+ characters = keep fire extinguisher handy