> At 9:58 PM -0200 12/7/97, Julio Gonzalez Cabillon wrote: > >At 07:47 PM 05/12/1997 GMT, Mark Snyder wrote: > >>I have heard that until about 1800, 1 was considered to be a prime number. > >>Is this correct? > > > >Not quite! JGC > > So what *is* correct? > > > mark snyder > I answered this at some length a few days ago. The tradition before this century (dating back to Euclid's Elements) was indeed to count 1 as a prime, and even Lehmer's 1914 list of prime numbers to 10 million does so. But the many inconveniences it causes have led people this century to put it into a new category, and call it a "unit" rather than a prime.