I realized an unusual property with $6 _{10}$, $5 _{8}$ and $9 _{16}$.
What these have in common is when you multiply them to an even number, you get the same 1's digit.
Here it is for base 10.
$6 \cdot 2 = 12$ $6 \cdot 4 = 24$ $6 \cdot 6 = 36$ $6 \cdot 8 = 48$ $6 \cdot 10 = 60$
and so on. It works for base 16 and base 8. I would imagine it working for other powers too.
Here it is for base 16. (As I'm doing this I'm seeing the same values, but in a different base, interesting...)
$9_{16} \cdot 2_{16} = 12_{16}$ $9_{16} \cdot 4_{16} = 24_{16}$ $9_{16} \cdot 6_{16} = 36_{16}$ $9_{16} \cdot 8_{16} = 48_{16}$ $9_{16} \cdot A_{16} = 5A_{16}$ $9_{16} \cdot C_{16} = 6C_{16}$ $9_{16} \cdot E_{16} = 7E_{16}$
Why is that? Its something like with $( B / 2 ) + 1$ where $B$ is the base.