If one tries to tessellate the sphere surface with solely hexagon. Let $x$ be the number of hexagon, then:
This leads to contradiction.
To make tessellation possible, we have to add $y$ pentagons, so that:
So we can solve and get $y = 12$.
So a sphere surface can be tesellated with 12 pentagons plus (many) hexagons.
See also: https://github.com/vraid/earthgen-old