Tony Vella said:

I regret that when you go into double digits your solution will provide: 1, 10, 11, 12 .......1a, 2, 20, 21, .... 2a, etc.

Yes I see your point. It's quite fiddly to separate numbers out of a string with a mix of numbers and letters.

Is there always just one letter at the end? Eg. 23k but **not** 27aa?

If there's just one letter then something like this formula in the 'Sorter' column might work?

Code:

=IF(ISNUMBER(0+RIGHT(A3,1)),TEXT(A3,"00000")&"_",TEXT(LEFT(A3,LEN(A3)-1),"00000")&RIGHT(A3,1))

It's along the lines of Berton's comment of adding 0s but by putting a non-numeric _ character at the end when there's no letter, it should stay as a non-numeric value so no danger of it losing the leading zeros.

However this won't work if you ever have multiple letters at the end (eg. 27ab).