If you look up any math term in Google, you likely get front page links to articles at Wikipedia and MathWorld. Both are usually very good, with the latter being more formal but having a Mathematica slant. (MathWorld is hosted by Wolfram Research, makers of Mathematica).
MathWorld has guest contributors but is otherwise closed content, unlike Wikipedia which is completely open. But as I found out last week, MathWorld does accommodate content suggestions. I completed the comment form twice for the Cuban Primes page, once for a typographical error and once for a factual error. I got a response noting the corrections a few days later. Not quite the turn-around of Wikipedia corrections, but still functional.
I can confirm the errors were fixed, though now I see the last modification time stamp wasn’t updated …