# Summing over indices

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.

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

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

If n is you list, more elegant than Sum:
Total[1 - 1 / n] Length[n]