My son is hyperlexic. Hyperlexia (https://en.wikipedia.org/wiki/Hyperlexia) is an autism-like disorder that is characterized by precocious reading ability. Mine was reading at less than eighteen months. He's now seven, and one of his relaxation activities is doing math problems --mostly simple ones.
One night, when he had worked his way through the workbooks my wife and I had bought him, he started bringing over his notebooks, and asking one or the other of us to "write math practise, addition and subtraction" at the top of a page, followed by at least thirty math problems. So we did.
For three hours.
When, thankfully, it was bedtime, we put him to bed and I looked through the workbooks and the rapidly filling notebooks. Inventing all those problems had been a giant pain. Pretending I'm capable of randomness after the first few dozen problems isn't easy. But then I had a thought. My son has a phone. He doesn't really use it for anything but youtube and texting my wife and I, but he has it. So...what about a site that would generate problems for him? Simple! Then I can just put a shortcut to it on the desktop, and call it a day.
Turns out, anyone putting that kind of thing online is going to be advertizing like hell to your kids. And, uh, no. So that night, after the boy went to bed and before I did, I whacked this together. the next day, when his BHP reached out through my wife, I said "sure, your other clients can use this if they want to." So now it's online. I'll tweack this as required, but it's honestly very simple. Have fun playing with it!