How to point out a typo in an equation in an article? In an article (from 2015) I came across a wrong equation with a sign error in one term. In the publicly available code, the correct sign is used, so the results of this particular paper are correct. However, several other papers have since copied and used this equation, and therefore likely have wrong results because of it. It won't change any conclusions I think, some results would change by a factor ~1.5. Should I just email the authors, or the journal? And what about the other papers that used the wrong equation?
Yes, you can email both the authors and the editor of the journal. A correction might be issued. But it is worth a bit of effort.
Of course, if it is obvious in the paper then it may be that it has been noticed by many and they have responded, or just ignored the error as obvious and moved on.
But it you have some evidence that the error has affected the results of newer papers then it might be especially important to reach out.