I found this info during a google search on the net.
Olympus later added an "N" designation to the OM1 and OM2, making them the OM1N and the OM2N. The "N" improvements were minor, allowing, for example, a 2 minute shutter speed and true off-the-film metering on the OM2 in automatic mode. "N" cameras don't seem to fetch much more than non- "N" models on the used market, so you should go for one, if you can -- you'll be getting a newer camera in the bargain.
Hope that helps.