Pi is the number found by dividing the circumference of a circle by its diameter. Because this number is the same for every circle, mathematicians call it a constant. As a decimal, pi is a number that goes on forever without repeating. Here’s how it begins, in case you want to memorize it:
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679 …