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I want to place a number or character inside $\sum$ to indicate the increment. So for example $\sum_{i=1}^8 i $ with 3 inside $\sum$ will indicate 1+4+7. How would I accomplish this?

This is to follow a convention in most programming languages that allow an array of equally spaced numbers to be created by using a syntax similar to start:increment:end.

Of course the index of summation can be redefined so as to accommodate any desired fix number but the readability may suffer.

  • I am not sure why you do not write $\sum_{i=0}^3 (2i+1)$. Or is that what you want to exclude with your last paragraph in the question? – Lucas Jul 22 '18 at 22:20
  • @Lucas Yes, while redefining the running index would be perfectly OK sometimes one ends up with expressions such as $\floor*{\frac{N}{m}}$ as the top value of summation and other artifacts. – Maesumi Jul 24 '18 at 15:53
4

Maybe this?

\documentclass[11pt]{article}
\usepackage{amsmath} 

\begin{document}

\[ \sum_{\substack{i = 1\\\text{step }3}}^8 i \]%

\end{document}

enter image description here

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