Let n denote a positive integer and let σ(n) denote the sum
of all divisors of n, so that σ(n) is larger than n (for n>1)
but not by much since it's bounded above by c nloglogn .
This invites comparison between situations in which the two are
interchanged. As an example, consider the following:
Let A be a subset of the positive integers. Suppose that
the sum of 1/n , for all n in A , converges. Then the sum
of 1/σ(n) , over all n in A, clearly converges as well.
Is the converse true?
No comments:
Post a Comment