The Riemann hypothesis is the most important open question in number theory—if not all of mathematics. It has occupied experts for more than 160 years. And the problem appeared both in mathematician ...

The internet is abuzz as the app formerly known as Twitter announced a name change last week. X.com now redirects to Twitter.com; the company's headquarters now sports a flashing X where there was ...

The letter “x” often symbolizes something unknown, with an air of mystery that can be appealing. Illustration by Meilan Solly Even though “x” is one of the least-used letters in the English alphabet, ...