Notes on type combination distribution

1. Normal: Least(2), Most(14), 9 on average.
2. Water: Least(4), Most(18), 8 on average.
3. Grass: Least(1), Most(8), 5 on average.
4. Psychic. Least(2), Most(10), 5 on average.
5. Fire: Least (2), Most(10), 4 on average.
6. Electric: Least(0), Most(6), 3 on average.
7. Normal/Flying: Least(1), Most(8), 3 on average.
8. Fighting: Least(1), Most(7), 3 on average.
9. Bug: Least(1), Most(5), 2 on average.
10. Fairy: Least(0), Most(9), 2 on average.
11. Poison: Least(0), Most(10), 2 on average.
12. Ground: Least(0), Most(6), 2 on average.
13. Bug/Flying: Least(0), Most(4), 2 on average.
14. Grass/Poison: Least(0), Most(9), 2 on average.
15. Ice: Least(0), Most(6), 2 on average.
16. Bug/Poison: Least(0), Most(5), 1 on average.
17. Dragon: Least(0), Most(4), 1 on average.
18. Rock: Least(0), Most(3), 1 on average.
19. Dark: Least(0), Most(4), 1 on average.
20. Rock/Water: Least(0), Most(4), 1 on average.
21. Rock/Ground Least(0), Most(6), 1 on average.
22. Ghost: Least(0), Most(4), 1 on average.
23. Water/Ground: Least(0), Most(4), 1 on average.
24. Steel/Psychic: Least(0), Most(4), 1 on average.
25. Water/Flying: Least(0), Most(2), 1 on average.
26. Grass/Flying: Least(0), Most(3), 1 on average.
27. Psychic/Flying Least(0), Most(3), 1 on average.

12+(7*2)+(3*3)+4+10+8+9=26+13+27=66 species.

Always appearing types:

1. Normal: Least(2), Most(14), 9 on average.
2. Water: Least(4), Most(18), 8 on average.
3. Psychic. Least(2), Most(10), 5 on average.
4. Fire: Least (2), Most(10), 4 on average.
5. Grass: Least(1), Most(8), 5 on average.
6. Normal/Flying: Least(1), Most(8), 3 on average.
7. Fighting: Least(1), Most(7), 3 on average.
8. Bug: Least(1), Most(5), 2 on average.

Common types:

1. Electric: Least(0), Most(6), 3 on average.
2. Fairy: Least(0), Most(9), 2 on average.
3. Poison: Least(0), Most(10), 2 on average.
4. Ground: Least(0), Most(6), 2 on average.
5. Bug/Flying: Least(0), Most(4), 2 on average.
6. Grass/Poison: Least(0), Most(9), 2 on average.
7. Ice: Least(0), Most(6), 2 on average.

Every once in a while types:

1. Bug/Poison: Least(0), Most(5), 1 on average.
2. Dragon: Least(0), Most(4), 1 on average.
3. Rock: Least(0), Most(3), 1 on average.
4. Dark: Least(0), Most(4), 1 on average.
5. Rock/Water: Least(0), Most(4), 1 on average.
6. Rock/Ground Least(0), Most(6), 1 on average.
7. Ghost: Least(0), Most(4), 1 on average.
8. Water/Ground: Least(0), Most(4), 1 on average.
9. Steel/Psychic: Least(0), Most(4), 1 on average.
10. Water/Flying: Least(0), Most(2), 1 on average.
11. Grass/Flying: Least(0), Most(3), 1 on average.
12. Psychic/Flying Least(0), Most(3), 1 on average.

To have 72 species in next generation (average 9 per generation):

1. Normal: +7

To have 64 species in next generation (average 8 per generation):

1. Water: +2

To have 40 species in next generation (average 5 per generation):

1. Grass: +2
2. Psychic: +5

To have 32 species in next generation (average 4 per generation):

1. Fire: +1
2. Electric: +5
3. Normal/Flying: +6

To have 24 species in next generation (average 3 per generation):

1. Fighting: +2
2. Bug: +6
3. Fairy: +8

To have 16 species in next generation(average 2 per generation):

1. Poison, Ground: +1
2. Bug/Flying, Grass/Poison, Ice: +2
3. Bug/Poison, Dragon: +4
4. Rock, Dark: +5
5. Rock/Water: +6
6. Rock/Ground, Water/Ground, Ghost: +7

To have 8 species in next generation(average 1 per generation):

1. Steel/Psychic, Water//Flying, Grass/Flying, Psychic/Flying, Steel: +1
2. Ground/Dragon, Rock/Steel, Bug/Steel, Psychic/Fairy, Water/Poison, Fire/Flying, Fire/Fighting, Dragon/Flying, Water/Ice, Ghost/Grass, Bug/Grass: +2
3. Poison/Dark, Electric/Flying, Normal/Fairy, Bug/Water, Bug/Rock, Dark/Flying, Grass /Fairy, Water/Dark, Water/Psychic: +3

To have 8 species in next generation(average 1 per generation):

1. Bug/Electric, Psychic/Fighting, Water/Fairy, Electric/Steel, Ground/Ghost, Normal/Fighting, Steel/Ground, Ghost/Fire, Dark/Dragon, Rock/Flying: +4
2. Normal/Psychic, Dark/Psychic, Ground/Flying, Steel/Fairy, Fire/Ground, Water/Electric, Grass/Steel, Dragon/Fire, Dark/Fighting, Water/Grass, Poison/Flying, Rock/Electric, Steel/Ghost, Dark/Fire, Fire/Psychic, Bug/Fighting, Ghost/Flying, Ghost/Poison, Ground/Ice, Ground/Dark, Grass/Fighting, Grass/Dark, Grass/Psychic: +5

Edit (19.01.2019): Moved Steel up due to Meltan-Melmetal