The name of a 99 sided polygon is enneacontaenneagon.
Applying systematic polygon names to regular polygons between 20 and 99 sides, a 21-sided polygon would be called an icosikaihenagon.
name of 4000 sided polygon
The name of a 51 sided polygon is Pentaconhenagon. The name of a 52 sided polygon is Pentacondigon. The name of a 53 sided polygon is Pentacontrigon. The name of a 54 sided polygon is Pentacontetragon. The name of a 55 sided polygon is Pentaconpentagon. The name of a 56 sided polygon is Pentaconheptagon. The name of a 57 sided polygon is Pentaconhexagon. The name of a 58 sided polygon is Pentaconoctagon. The name of a 59 sided polygon is Pentaconenneagon.
That would depend on what A sided polygon it is.
The name of a 100 sided polygon is Hectogon.
The name of a 14 sided polygon is Tetradecagon.
The name of a 200 sided polygon is dihectagon.
The name of a 18 sided polygon is Octadecagon.
The name of a 8 sided polygon is Octagon.
The name of a 20 sided polygon is Icosagon.
The name of a 395 sided polygon is trictoeneapentagon.
The name of a 600 sided polygon is Hexcosiagon.