Ancient Egyptians built their pyramids using large stone blocks, but mathematicians only need numbers - specifically, palindromic prime numbers - to build these interesting mathematical pyramids.
G.L. Honaker, Jr. of Bristol Virginia Public Schools and Chris K. Caldwell of University of Tennessee at Martin start with the simple pyramids above, centered on the prime number of 2 ...
Then they got serious:
See how they did it: Palindromic Prime Pyramids [PDF] - via Cliff Pickover