I found something, but I'm not sure what it is. Summation Notation
Epsilons, no. 6: What is that Σ? - by Tivadar Danka
Positioning limits above and below a summation in LaTeX/Overleaf - YouTube
math mode - Alternative sum symbol for Neo Euler - TeX - LaTeX Stack Exchange
math mode - What is the command for a sum symbol superimposed on an integral sign? - TeX - LaTeX Stack Exchange
File:Latex math example substack sum.png - Wikimedia Commons
How to use sigma, summation(Σ) symbol in LaTeX?
Sigma or summation (∑) in LaTeX - CodeSpeedy
Iverson bracket - Wikipedia
What is the latex code for writing a condition under the subscript of a sum? - TeX - LaTeX Stack Exchange
math operators - LaTeX adjusting \sum limits - TeX - LaTeX Stack Exchange
Latex Math Symbols
Sigma and Pi Notation (Summation and Product Notation) – MathMaine
1,080 Summation Symbol Images, Stock Photos, 3D objects, & Vectors | Shutterstock
How do you use summation(∑) in LaTeX? | Sigma symbol
The Sum Operator: Everything You Need to Know - Probabilistic World
Sum in Math equation editor - Microsoft Community
7.2 "Sigma notation" for sums - YouTube
How to use power or superscript(a²,xⁿ) in LaTeX? | Latexhelp
6. Large operators | LaTeX manual
math mode - making a big summation sign - TeX - LaTeX Stack Exchange
How do you use summation(∑) in LaTeX? | Sigma symbol
How do you use summation(∑) in LaTeX? | Sigma symbol
math mode - making a big summation sign - TeX - LaTeX Stack Exchange
How to write Sigma(∑,σ) symbol in LaTeX?
