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

  • 2
    $\begingroup$ 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, 2019 at 9:20
  • $\begingroup$ Yes. That is right. $\endgroup$
    – user120911
    Aug 23, 2019 at 9:30
  • $\begingroup$ Cool, I'll add it as an answer to the original post. $\endgroup$
    – Fraccalo
    Aug 23, 2019 at 9:52
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    $\begingroup$ What about Nmax Total[1 - 1/n]? $\endgroup$ Aug 23, 2019 at 14:35

2 Answers 2


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.


If n is you list, more elegant than Sum:

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

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