Having computer access in the digital age isn't a luxury anymore — it's a basic human need. For low-income families and individuals, finding free personal computers can be difficult. Only so many ...

The original version of this story appeared in Quanta Magazine. Imagine that someone gives you a list of five numbers: 1, 6, 21, 107, and—wait for it—47,176,870. Can you guess what comes next? If ...