Thursday is the annual Pi Day (because Americans would write the date 3.14).
This year, Marcus du Sautoy is hosting Pi Day Live. It's a free interactive online event that is open to all.
The number pi has intrigued mathematicians throughout the ages and this fascination has shown no sign of stopping. In recent times mathematicians have employed super-computers to calculate pi to over a trillion decimal places.
In Pi Day Live, Marcus du Sautoy will be asking whether the techniques used by the ancients to calculate pi can still be used today. And if so, which ones are best? As a part of the interactive audience, you will be a part of answering these questions and more.
To take part, visit the event's online lecture theatre, or go to the event's big screen to watch online. All you need is access to YouTube to get involved.