Which Numberblock Series is best for 4 year old?

I started getting my 4 year old to watch number blocks and the earlier episodes up to 10 seem to be too easy.

Should i start from Series 3 where they start going from 11 and above? Some of the Series 4, do start doing some advanced math like 18 can be 3x6 or 2x9 so I don't think its suitable.

What do y'all recommend.