PI

PI returns the number 3.14159265358979, the mathematical constant pi, accurate to 15 digits.
Sure, you rememebr these, but this one is typed faster, innit?

=PI()Pi (3.14159265358979)
=PI()/2Pi/2 (1.570796327)
=PI()*(3^2)Area of a circle, with the radius (28.27433388)