The pi symbol isn't readily available on your iPhone's default keyboard, but there are tricks you can do to change that and have it available whenever you need.

You can add special characters on a PC or Mac computer by using keyboard shortcuts or accessing a pop-up window.

On Windows 10, you can use your keyboard to quickly add emoji, kaomoji, and symbols to messages or documents, and in this guide, we’ll show you how.

The QuickType keyboard on the iPad has been updated in iOS 11 to introduce a super handy new Flick feature designed to let you enter numbers and symbols without the shift key.