>Probably this is well known.
>http://www.freepatentsonline.com/5373560.html
>http://mathworld.wolfram.com/PrimeNumber.html
>(check (3))
>> Because of their importance in encryption algorithms such as RSA encryption, prime numbers can be >>important commercial commodities. In fact, R. Schlafly (1994) has obtained U.S. Patent 5373560 on the >>following two primes (expressed in hexadecimal notation): 

>fuck, fuck, fuck.

To repeat what ought to be well-known, in order to be patentable, an invention must be:

1.   New

2.   Useful

3.   Unobvious to those skilled in the art.

Those two primes were clearly not 'new'.  (The knowledge by humans that those primes WERE primes may have been new, however.  But I don't think that qualifies.)

Arguably, these primes are 'useful'.

However, these numbers (to the extent they are primes) are indeed 'obvious' to those skilled in the art.

Also, I believe there is a rule that says that laws of nature aren't patentable.  To the extent that primality is a law of nature, it shouldn't be patentable.  

The good news is that patents last 20 years these days.  If the patent was granted in 1994, it either has run out or shortly will do so.

             Jim Bell