[pbhjpbhj]

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.

[gfredtech]

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