Just to make it even easier, here's what the "**By Numeric**" rollout in the Graphite Ribbon looks like close up.  Just click on the "equal to", "smaller than", or "greater than" buttons, and then click the arrow to automatically select all of those faces on your mesh.  Obviously, there is the ability to change the number of sides, if you wanted to be more specific.

Some UI configurations in Max can make the Ribbon appear differently, on different display types, but this is the panel you're looking for, and will appear under the "Selection" tab, when you have Polygon subobject mode enabled. 

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