Pascal's Triangle (idea)

One might also find it interesting the relationship of Combinations (_nC_r), and Pascal's Triangle. For each row, n of the triangle (top row being 0), each element along that row, r, is == _nC_r.

          1
        1   1
      1   2   1
    1   3   3   1
  1   4   6   4   1 <-- n=4



 Combinations of 0: 1
  1: empty set

 Combinations of 1: 4
  1: A
  2: B
  3: C
  4: D

 Combinations of 2: 6
  1: AB
  2: AC
  3: AD
  4: BC
  5: BD
  6: CB

 Combinations of 3: 4
  1: ABC
  2: ABD
  3: ACD
  4: BCD

 Combinations of 4: 1
  1: ABCD