2 (two)
In mathematics, the number 2 has a very special place.
Explanation
The first numbers are 0 (which stands for nothing) and 1 (which stands for something), then follows immediately 2 (which stands for more). This means that there is more than just one thing. The step from 1 to 2 opens the way to choices, propagations, to variations, etc.
A good example is the difference between black and white television or color television.