Learn LaTeX! You can write math and read the source with a screen reader. Here is a tutorial: http://www.math.harvard.edu/texman/

Reminds me of me and my friend /u/graham87 when we were that age. Playing with calculators to learn how things work, etc.

Blind people into math exist, but there aren't a lot of us – especially as you get into higher levels. Sadly, this means that schools for the blind will limit his potential when he gets to a certain point.

I'd say let him keep exploring and learning. My story is unique, in that I discovered a set of batch file commands online at around age 8 and started exploring from there, writing simple computer programs and such. If he isn't familiar with screen reading (or, in his case, magnification) software, give him access to tutorials. JAWS, for example, includes a set of training tapes. Let him play them, give him access to a machine with a screen reader (even the 40-minute demo, which is what I had, as the school said I was "too young" for the computer) and let him experiment at his own pace. I'm not sure how much (or if) you should guide this process, as most of it was self-exploration in my case.

I, like /u/codeofdusk, was really into maths as a kid ... I loved playing with numbers and doing mental calculations. Does your son have a Braille notetaker or talking/Braille calculator? If so, encourage him to mess around with it and play with its commands/functions. This sort of experimentation is how we learnt about decimal points and negative numbers long before they were covered at school. I mention Braille notetakers/talking calculators because the Windows calculator only works well with JAWS, and only with versions of Windows below Windows 10, and I don't know of a well-documented alternative for Windows.

Can he see at all? $1 is a graphics-based programming 'language' that was designed by MIT to help teach kids to code. I bet the'd have some fun with that.

You can also get legos to help him with his spatial reasoning skills.

It may also be worth cross-posting to r/teaching or r/matheducation or subs like that to see if any teachers have direct experience or advice for you.

Also, you should be aware that the math education system in the US is utter garbage. A kid at 7 that is into math is kinda rare, please try to encourage him as much as possible and not let the awful machine that is US public education beat it out of him.

What is his age?

Did you knew that the greatest mathematician of all time went blind? After he went blind he started the most prolific time of his life.

His name was Euler.

There are a lot of interesting $1 workbooks on a variety of subjects and their $1 is reportedly quite good.

As a totally blind guy who's always hated math with a burning passion, I could be wrong here but I think braille is really important for math in a way it isn't these days for other things. I always felt with math that I had to 'see' not hear a problem, and I could only do that with braille. So I guess my biggest advice is just to make e he learns all the braille related to math. Beyond that the advice is the same it would be for sited people. Find math books and games. You could go buy him a math textbook for where he is so he could keep learning on his own.