I'm trying to find a general formula for a harmonic(ish) series

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Discussion Overview

The discussion centers around finding a general formula for the partial sum of a series defined by the nth term as a_n = 1/(c+kn), where c and k are arbitrary constants. Participants explore the relationship of this series to the harmonic series and the nature of its convergence.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks a general formula for the partial sum of the series a_n = 1/(c+kn).
  • Another participant questions whether the original inquiry pertains to the sum or the partial sums, noting that the series is divergent.
  • Clarifications are made regarding the specific interest in partial sums rather than the overall sum.
  • There is a suggestion that the participant may be looking for a formula similar to that of the harmonic series.
  • A later reply indicates that what was thought to be a formula is actually only an approximation, prompting a request for clarification on the specific example.
  • One participant proposes a formula for the partial sum using the notation f(m;c,k) = Σ (from n=1 to m) 1/(c+kn) and provides links to external resources.
  • Another participant expresses uncertainty about the existence of a closed form for the standard harmonic series, mentioning Bertrand's lemma as a relevant theorem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the existence of a closed form for the series or the nature of the approximation discussed. Multiple views regarding the relationship to the harmonic series and the specifics of the formula remain present.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the constants c and k, as well as the unresolved nature of the mathematical steps involved in deriving a formula.

al4n
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Im looking for a general formula for the partial sum of a series where the nth term is in the form of
a_n = 1/(c+kn),
where c and k are arbitrary constants.

it "looks" like a harmonic series but not in the form I'm capable of figuring out.
help.
 
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Do you mean the sum? It is divergent! Or do you mean the partial sums? Or something else?
 
martinbn said:
Do you mean the sum? It is divergent! Or do you mean the partial sums? Or something else?
my bad I wasn't specific enough. I meant the partial sum.
 
al4n said:
my bad I wasn't specific enough. I meant the partial sum.
What is that for the harmonic series?
 
martinbn said:
What is that for the harmonic series?
what do you mean?
 
al4n said:
what do you mean?
Well, you said.
al4n said:
it "looks" like a harmonic series but not in the form I'm capable of figuring out.
help.
It sounds like you can figure out the case of the harmonic series, and want to do the same with the more general. Is it not what you mean?
 
martinbn said:
Well, you said.

It sounds like you can figure out the case of the harmonic series, and want to do the same with the more general. Is it not what you mean?
I guess. Is that not already figured out? Looking around, What I thought was the formula was in fact only an approximation. So what I should've first asked is, is there something like that to the specific example
 
al4n said:
I guess. Is that not already figured out? Looking around, What I thought was the formula was in fact only an approximation. So what I should've first asked is, is there something like that to the specific example
So to be clear: you are looking for a formula for ##f(m;c,k)=\displaystyle{\sum_{n=1}^m}\dfrac{1}{c+kn}## for any parameters ##c,k \in \mathbb{R}##?

In that case, the answer is
https://www.wolframalpha.com/input?i=sum+(from+n=1+to+m)+1/(c+kn)=
https://en.wikipedia.org/wiki/Polygamma_function
 
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I'm not aware of the existence of a closed form for the ( Standard) Harmonic, only that the partial sums are never Integers. Uses Bertrand's lemma, which I believe it is now a theorem.
 

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