Is Absolute Convergence Required for Evaluating Sums over Rational Numbers?

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Discussion Overview

The discussion centers on the evaluation of sums over the set of rational numbers, specifically considering whether absolute convergence is necessary for such evaluations. Participants explore various functions and series involving rational numbers, primes, and their properties.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes evaluating sums of the form \(\sum_{q} f(q)\) where \(q = \frac{m}{n}\) and \(m, n\) are positive integers.
  • Another participant suggests that since the rationals are countable, it should be possible to evaluate such sums.
  • Concerns are raised about the dependence of the sum on the ordering of rational numbers, which can be influenced by their correspondence with positive integers.
  • A participant questions whether expressing \(m\) and \(n\) as products of primes allows for considering series over primes or prime powers, proposing the sum \(\sum_{m=-\infty}^{\infty}\sum_{p}f(p^{m})\) as a potential approach.
  • It is noted that using suitable products of primes can reproduce every positive rational number, leading to the exploration of 'invariant-under-dilation' formulas.
  • Another participant asserts that all rearrangements of a series converge to the same value if and only if the series is absolutely convergent, indicating that this could affect the sum being evaluated.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of absolute convergence for evaluating sums over rational numbers, with some supporting the idea while others raise concerns about the implications of ordering and convergence properties.

Contextual Notes

Participants do not fully resolve the implications of absolute convergence on the evaluation of sums, and there are unresolved questions regarding the dependence on ordering and the properties of the functions involved.

zetafunction
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it is possible to evaluate sums over the set of Rational

so \sum_{q} f(q) with q= \frac{m}{n} and m and n are POSITIVE integers different from 0 ??

in any case for a suitable function is possible to evaluate

\sum_{q} f(qx) with f(0)=0 ??
 
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I would think so, as the rationals are countable.
 
However, in some cases the sum will depend on the ordering of the rational numbers given by the one-to-one correspondence with the positive integers.
 
um.. if i use the fundamental theorem of the arithmetic to express m and n as a product of primes could i write or consider at least series over prime or prime powers ? i mean

\sum_{m=-\infty}^{\infty}\sum_{p}f(p^{m})

in both case this sum is over prime and prime powers is this more or less correct ??

using suitable products of primes we can reproduce every positive rational can't we ?

so we can study 'invariant-under-dilation' formulae as follows

\sum_{m=-\infty}^{\infty}\sum_{p}f(xp^{m})
 
HallsofIvy is correct: all rearrangements of a series converge to the same value if and only if the series is absolutely convergent. So that can affect the sum.
 

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