Thursday, 9 August 2012

Factorials

This is the sequence of factorials. Each factorial is made by putting it and all the numbers before it into one big tower. Here is the number line from 1 to 9.

By looking at the colours one at a time, you can work out how many blocks of each colour there is in a factorial. Here are only the blue blocks in the number line from 1 to 20

The number of blue blocks in n factorial is
$\lfloor \frac{n!}{2} \rfloor + \lfloor \frac{n!}{4} \rfloor + \lfloor \frac{n!}{8} \rfloor + \ldots$