I expected slightly smaller "small primes" :-) And I stand corrected regarding the sparseness of primes. Thanks, you never stop learning :-)

(For a minute I thought whether it wouldn't be better to generate just one random number and then keep subtracting/incrementing until you find a prime, so that the algorithm is garanteed to finish, but that's not a good idea. Primes are not evenly distributed so some would come up more often than others.)