Ehm... Sorry, Cheesehawk, but I'm sure Cpt.Doggles' formula is right
. It's a simplified, basic formula for prop thrust, obtained from the definition of prop efficiency, which can be found in any book about props... or on the same page You linked to, just a couple of lines below the formula You quoted. Note the formula being used for thrust estimation in the numerical example at the bottom of the same page.
Cheers - Art