One of the very first things in maths I taught my kids -- after they could count to 20 -- was binary ("robot numbers!") and from there alternate number bases [stuck well with the first, not so well with second, not at that point with any others]. Think that came from the same place as "what if there's no 6".

I took the approach of how aliens would count if they didn't have "enough" fingers.

Someone told me that once; perhaps the reason we naturally count in base 10 is because we have 10 fingers. If there was no six, I also think that we'd be counting in base 5

6 still "exists" in base 5, it's just that it equals...ahem...is congruent to 10.

So take it out, you end up with a set of previously-numbers objects you can't do much with. The question is answered.

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