On February 23, 1855, one of the greatest mathematicians of all time died in Göttingen, Germany. He requested that a heptadecagon - a regular 17-sided polygon - be carved on his tombstone. He was proud that he had given a proof of its construction. Unfortunately the stone mason declined saying the figure was too complex.
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Note: Modern stone masons can reproduce a picture of the heptadecagon, or almost any image, by using a laser and computer software.