Figurate number that can be represented by sets of points arranged on the edges of a regular tetrahedron or by a sequence that is partially interlocked with regular tetrahedrons.

- The sequence of pyramidal numbers is: 1, 4, 10, 20, …, \(\dfrac{1}{6}\)
*n*(*n*+ 1)(*n*+ 2) where*n*corresponds to the number of points on an edge of the pyramid. - The pyramidal numbers are also called
**tetrahedral numbers**.