Answers are grounded in this paper and cite their sources.
The function a (n) = dInd is the sum-of-divisors function, so for example a (6) = 12. The number Hn is called the nth harmonic number by Knuth, Graham, and Patashnik [12, sect. 6.3], who detail various properties of harmonic numbers. The 'E' in Problem E might stand for either 'easy' or 'elementary'. Perhaps 'H' for 'hard' would be a better letter to use, since our object is to show the following equivalence.
No takes yet. Share an insight, caveat, or question.
Jeffrey C. Lagarias (2002) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: