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'Light the Lights Again' printed from http://nrich.maths.org/
This problem is similar
to Light the Lights, but slightly more tricky.
You may like to try that one first.
Here is a machine with four coloured lights. Each light responds to
When you type in a number, lights go on if their rule is satisfied.
If the number satisfies more than one rule, then more than one
colour will light up.
Type in some numbers and see which lights you can switch on.
What is the smallest number which lights up all the lights?