Possible idea:
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Define r=1/c
Define sum[1/i] i:2->n = sumH(n)
If k*r for any integer k>1 equals any 1/i then k and i are solutions
Choose starting point x such that 1<x<c
Choose a range over which to search e.g. 100 consecutive numbers
Calculate starting remainder r(x)=x/c
Calculate sum of remainders for c, S_r=r(x)+(100-1)*r
Calculate sum of harmonic series for same range S_h=sumH(x+100)-sumH(x)
Evaluate S_r,S_h
If all 100 consecutive numbers are factors of c then S_r-S_h=0
Where I am stuck is what if none of 100 numbers are factors?
What is some relation with S_r,S_h in that case? We know c.
If we figure this out we can construct a log(n) algorithm. Half the search space when match found.