I put a handful of pennies on the table and I wondered whether I could group them so that each penny touched three and only three of the others. It took a while but I found it was possible. I then wondered whether I could do it with fewer pennies. It was clear that I could not.

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## bonanova

I put a handful of pennies on the table and I wondered whether I could group them so that each penny touched three and only three of the others. It took a while but I found it was possible. I then wondered whether I could do it with fewer pennies. It was clear that I could not.

How many pennies were in the group?

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