Wolfram Research
Wolfram Math World: Pascal's Triangle
This site from MathWorld provides great information on Pascal's Triangle. Links are provided throughout for additional information, along with several helpful charts and formulas. This is a good site to check out on the subject.
Mathigon
Mathigon: Algebra: Figurate Numbers
There are many other sequences that are based on certain geometric shapes. These sequences are often called Figurate numbers, numbers that can be represented using geometric shapes. Examples include square, triangle, and tetrahedral...
Wolfram Research
Wolfram Science World: Pythagoras of Samos (Ca. 560 Ca. 480 Bc)
This site from ScienceWorld provides a short, informative description of many of the contributions of Pythagoras to mathematics. Links exist to some of the contributions as well as to additional information.