Well apparently that captcha is for Akademgorodok forums, Akademgorodok being kind of scientific city in/near Novosibirsk, so that math is quite understandable and most people logging onto those forums will be able to understand that captcha.
Curiously I can't find it on the forums now, but the forum software looks different now too.
btw, the text on left of image reads "Protection from automatic registration" and text above box says "Insert answer", it's your standard forum software.
Also that screenshot is horrible. Had to invert colours and turn up contrast before I could read some of text, and I'm normally good at reading low-contrast-difference text.