This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Pyramides quadratae secundae.svg en en Octahedral numbers represented as square pyramids in which each layer has centered square number of units own David Eppstein Cczero Figurate numbers Files by User David Eppstein from en
Page 2023 Free-images.com. All images are Public Domain