## 15 April 2017

### Five

$5$ is the only prime number ending in $5$.

There are $5$ platonic solids: tetrahedron, cube, octahedron, dodecahedron and icosahedron.

$5$ is a congruent number because equates the area of a right-angled triangle whose side lengths are rational numbers: $\frac{20}{3}$, $\frac{3}{2}$ and $\frac{41}{6}$.

A pentagon has $5$ diagonals, being the only polygon where the number of sides is equal to the number of diagonals.