Grasshopper is sitting at point of coordinate line. He makes jumps in positive direction. Firstly his jump has length , every next jump is times longer than the previous one. There are holes in every point with coordinate , . Determine for which the grasshopper will make all the jumps and will not jump into hole.
Solution
We have to find such , for which is not divisible by .
Let us suggest that . As we see, every coordinate after the jump has residue modulo thus cannot be divisible by . So all such are the answers.
If , let us look at all the residues of modulo . If at least one value has residue then does not satisfy the condition. Let us suggest that there are no zeroes, then at least two residues are the same. Let them be and , . Their difference is divisible by , but then
Thus is divisible by , and we have a contradiction.
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