"djbroadhurst" <d.broadhurst@...> wrote:

> We can use one prime in F = {3,5} to wipe out the other:

More generally, if F = {q,r} contains two distinct odd primes,

> p = 15*x + 19. Then 3 divides 38-5 and 5 divides 38-3:

> mutual annihilation :-)

then any one of the infinity of primes of the form

p = q*r*x + (q+r)/2 solves the problem, since

q divides 2*p-r and r divides 2*p-q.

David (speaking minimal Chinese:-)