I have a number machine.
I say x gives y if when x goes in, y comes out.
For any numbers x and y, by "xy" I mean x followed by y.
Here are my two rules.
1x gives x.
For example, 13 gives 3.
If x gives y, then 2x gives yy.
For example, 213 gives 33 since 13 gives 3.
What is a number that gives itself?
Let x>y mean "x gives y."
121>21
2121>2121
Therefore, 2121 gives itself.

Posted by Math Man
on 20140623 20:32:09 