1k+2k+3k+...+nk is divisible by 1 + 2 + 3+... n for every nϵN, then k is:
A
even
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B
odd
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C
only prime
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D
none of these
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Solution
The correct option is B odd Check for different values of k. 11+21+31+411+2+3+4=113+23+33+431+2+3+4=10010=10 and so on. You can consider some more examples and then you will find that only choice (b) is correct.