π=3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 70679 82148 08651 32823 …
A sphere has two sides. However, there are one-sided surfaces.
There are shapes of constant width other than the circle. One can even drill square holes.
There are just five regular polyhedra
In a group of 23 people, at least two have the same birthday with the probability greater than 1/2
Everything you can do with a ruler and a compass you can do with the compass alone
Among all shapes with the same perimeter a circle has the largest area.
There are curves that fill a plane without holes
Much as with people, there are irrational, perfect, complex numbers
As in philosophy, there are transcendental numbers