What is the probability of getting a royal flush in Texas hold'em.

[magnus2022]

There have been argument abour the probability of getting a royal flush in Texas hold'em. Some said it is 1 in 649739 ie around 0.000154%. But from my poor understanding of math, it is impossible to get the probability without taken into consideration the number of players at the table. Can somebody explain the math behind this probability for me.