[...snipped...]
[/quote]
Thanks for explaining it but i dont get what is the number 95823 from your first line
old_key = 4563 -- was from "95823/21"
[/quote]
95823 was from 1764F on 17 bit puzzle, 17 bit into 21 bit.
"How many multiples are there from 95823 to 2097151?"
95823/2097151 = 21 = 4563.