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?

(In reply to re: Solution by Gamer)

What's with the last line: "This number must be 21, so 121 gives itself"?

The line preceding that gave a correct answer, "2121 gives 2121".

Posted by Charlie on 2003-06-08 05:02:57