A regular twenty-sided polygon is called an icosagon.
the name of a 20 sided 3d shape is called a icosahedron
One example is an icosahedron.Actually, it has to be an icosahedron - the name means a polyhedron with 20 faces!
A 7 sided shape is a heptagon
dodecagon
Decagon
pentadecahedron
Isasakaitateragon
pentagon
hexagon
heptagon
nonagon
An octagon.