Prime magnitude and keys...a ?

[Jim choate]

Hi everybody,

I was wondering if anyone is aware of a function or test which would allow
a person to feed PGP or other RSA algorithm a test key and then look at
the result and determine if the key was greater or lesser than the 
actual key? 

I am looking through several books and so far have come up with nada. I 
was hoping that somebody more familiar w/ the field would offer a suggestion.

Thanks for you help ahead of time...