>>>>Complete this serie:
>>>>
>>>>1
>>>>11
>>>>21
>>>>1211
>>>>111221
>>>>?
>>>
>>>The next "number" is 312211.
>>>
>>>How about this other series:
>>>
>>>

>>>10
>>>11
>>>12
>>>13
>>>14
>>>15
>>>16
>>>17
>>>20
>>>22
>>>24
>>>???
>>>100
>>>121
>>>10000
>>>

>>>
>>>BTW, I understand the word "Series" is both singular and plural.
>>>
>>>Hilmar.
>>
>>31
>
>Fascinating - it seems you know all of them!
>
>OK, for the benefit of other readers - the series represents the number "16", in different number bases: base 16, base 15, ... base 2.

The first one I knew, incidentally, I was playing number games with my 10 year old son & used that series. He rapidly guessed the solution & added that the series can only consist of the numbers 1 2 & 3.

The 2nd I was just lucky on, after looking at the numbers I thought they must be some other base than 10 & it took me a bit longer to realise that they were all different bases.