Pascal's Triangle
The figure below, extended infinitely.
A particular entry is found by adding the two numbers that are
above and on either side of the element. Note: The numbers which
make up Pascal's triangle are called binomial
coefficients.
Pascal's Triangle
Note that the sum of
any two adjacent elements
in a row can be found
between them on the next row. Each row begins and ends with
1. 

etc.

See also
Binomial coefficients
in Pascal's triangle, binomial theorem
