Help with explosive yield formula

[GraveDigger84]

Was attempting to use the explosive yield formula to calc this feat

After talking with Nike and Apollo, Leo had been certain that such an explosion would kill any mortal within a quarter of a mile, so he knew he would have to get far away from everyone.

Tried using this equation: W = R^3*((27136*P+8649)^(1/2)/13568-93/13568)^2

Using a R of 402.335 and a P of 1.37895 (instant fatalities for everyone), I inputed it into the calculator like this and got a very low number:

Am I inputting it wrong?

EDIT: SOLVED