The number of evenly spaced dots needed to make a square is a square number. This is just one kind of polygonal number . The same site proves that there are an infinite amount of numbers that are both square and triangular . Back to Top Tetrahedral Numbers Tetrahedral numbers are one kind of figurate number . They are found by counting the number of evenly spaced points needed to build a tetrahedron.
Tetrahedra are pyramids with triangular bases.
A triangular number is the number of dots needed to draw a triangle. This is one kind of polygonal number . Formula for Triangular Numbers Triangular Numbers Identifying triangular numbers, and one way to use them. I An Algebra Problem of the Week. Mrs. Pascalini's Garden A Middle School Problem of the Week.