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As in:

$$\sum_{i=1}^n r^i$$

It seems that $i$ is very frequently the subscript of choice in summations. Is there a historical/etymological reason why $i$ specifically is the default? Especially since $i$ already has an alternative mathematical meaning as a commonly used constant? I mean, I would never use $e$ as a variable. Why $i$?

Him
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    https://stackoverflow.com/questions/4137785/why-are-variables-i-and-j-used-for-counters – leonbloy Sep 13 '21 at 00:11
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    @leonbloy yes, I actually found this question on StackOverflow, saw that the most satisfactory answer was "because of math", and that the CS folks were satisfied with that. However, I suppose there must be some history for it in the math community as well, eh? "Because math" isn't exactly a satisfactory answer on MathStackExchange. :) – Him Sep 13 '21 at 00:14
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    In some branches of math, $e$ is used as a variable – for example, in computability theory, which deals with integers and only rarely with the transcendental number $e$. Similarly, $\sigma$ and $\pi$ are used in various fields as variables for permutations and other functions, despite their specialized meanings in statistics and analysis. Context is everything. – BrianO Sep 13 '21 at 01:33
  • Maybe because it is the first letter of the word index. – soupless Sep 22 '21 at 07:53

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