Select Nth Pattern

The n variable is the internal polygon number (which can be seen if you use the Info tool) and the offset variable is counted from that initial selection. If you select every 5th polygon in n this tool will get the first poly, the 6th, the 11th etc. If you have an offset of 1, it gets the second poly, the seventh, the twelfth, etc. The internal polygon number can be referenced from the Selection Info panel.