A Geometric Proof of the Square Pyramidal Number Formula
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.
"A Geometric Proof of the Square Pyramidal Number Formula"
Wolfram Demonstrations Project
Published: January 25 2008