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Suppose I have a simple equation with indices, like the one shown in the image. How can I use Mathematica to implement it? I am aware of summing when a specific variable changes value of some range, but the stated problem is different. Here the index references to a location in a list, and the value in that list can be many things.

enter image description here

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    $\begingroup$ do you mean something like: Sum[((n[[j]] - 1) Nmax)/n[[j]], {j, i, Nmax}], where n is a list with at least Nmax elements? $\endgroup$ – Fraccalo Aug 23 '19 at 9:20
  • $\begingroup$ Yes. That is right. $\endgroup$ – user120911 Aug 23 '19 at 9:30
  • $\begingroup$ Cool, I'll add it as an answer to the original post. $\endgroup$ – Fraccalo Aug 23 '19 at 9:52
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    $\begingroup$ What about Nmax Total[1 - 1/n]? $\endgroup$ – Henrik Schumacher Aug 23 '19 at 14:35
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Converting comment into an answer:

Sum[((n[[j]] - 1) Nmax)/n[[j]], {j, i, Nmax}]

, where n is a list with at least Nmax elements.

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If n is you list, more elegant than Sum:

Total[1 - 1 / n] Length[n]
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