Once you get below about 25 plants in a 4x4 block or a couple of containers, self pollination becomes an issue. You should hand pollinate if you have a smaller amount. Otherwise you risk having very poorly developed ears of corn.

I wanted to do only 6 corn plants due to lack of space and the fact that I dont want 200 ears of corn at the end of the growing season. I was told very quickly that it wont work. I would go ahead and plant a large amount to ensure you get a good crop.

I've grown smaller amounts of corn with great success when I helped with pollination. Just broke off a few parts of several tassels when they were shedding pollen and gently rubbed them over the silks on the young ears. Look carefully since you want to do this when the ears are small and there may be more than one on a plant. I repeated this several times over a few weeks....basically whenever I happened to be out there and thought of it. I've seen directions detailing time of day and using pollen bags and paintbrushes but this simple method worked for me at a garden that was not at my home. The ears were well filled with kernels and the ones the raccoons didn't get tasted great!