This is the final set of numbers and as you’ve probably guessed they’re based on the numbers 1-9 added to ‘Viṁśatiḥ‘ (20). In Primary Series you’ll only ever go up to the number ‘Aṣṭāviṁśatiḥ‘ (28) but John’s included the two numbers after that (29/30) so you can see the full progression.
So really, all you need to know are the numbers 1-9, 10 and 20 and how to combine them together!
Ekam + Vim = Ekaviṁśatiḥ
1 + 20
Dwe + Vim = Dvāviṁśatiḥ
2 + 20
Trini + Vim = Trayoviṁśatiḥ
3 + 20
Catvari + Vim = Caturviṁśatiḥ
4 + 20
Panca + Vim = Pañcaviṁśatiḥ
5 + 20
Sat + Vim = śaṭviṁśatiḥ
6 + 20
Sapta + Vim = Saptaviṁśatiḥ
7 + 20
Astau + Vim = Aṣṭāviṁśatiḥ
8 + 20
Ekoo + na + trim + sat = Ekonatriṁśat
(1 down from 30)
Trini + Sat = Triṁśat
3 x 10 = 30