How many Pokemon regions are there?

First of all:

1: Kanto

2: Orange Archipelago

3: Johto

4: Orre

5: Hoenn

6: Battle Frontier (Kanto/Hoenn)

7: Fiore

8: Sevii Islands

9: Sinnoh

10: Distortion World

11: Mystery Dungeon Realm (for Red and Blue Rescue Team, and Explorers of Time; Darkness; and Sky

12: Battle Frontier (Sinnoh/Johto FOR HEART GOLD AND SOUL SILVER)

13: Almia

14: Oblivia (for Pokemon Ranger Path of Light)

15: Duelist (for Pokemon Trading Card Game) (GAME BOY COLOR)

16: Stadium Island (for Pokemon Stadium)

17: White City: region N/A (for Pokemon Stadium 2)

... and finally, Drumroll, Please!

18: Poketopia (for Pokemon Battle Revolution)