Suppose I want to search for instances where an expression similar to $x_n^2-x_{n-1}x_{n+1}$ shows up. How would I do that?
I suppose the question goes beyond searching MSE. Are there search engines which handle math formulas in a particularly effective way?
Edit: I am listing some leads in the comments which I found useful:
Uniquation, a mathematical formula search engine. And here is the response to my query above. Perhaps this can be an option on MSE.