A Geometric Proof of the Square Pyramidal Number Formula

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The pyramidal numbers 1, 5, 14, 30, … are the sums of the square numbers, . This Demonstration shows a geometric proof of the square pyramidal number formula, . In the figure the six pyramids of side length form an cuboid.

Contributed by: Okay Arik (January 2008)
Open content licensed under CC BY-NC-SA




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