Finding equivalence relation with x amount of pairs

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Set X = {1, 2, ..., n} where n>200

Can I find relation R such that there are n-1 pairs? How about n, n+1, n+2, n+3 and n(n-1) pairs?

If not, how would I prove that there can not exist equivalence relation R such that the number of pairs is one of the above quantities without using contradiction or contrapositive proof?

I've thought about a relation where (x-y)=1 for n-1, but I don't believe its reflexive so its not an equivalence relation.