Convert integer to char equivalent – 1 = a, 2 = b, 27 = za

I want to convert an integer into its character equivalent based on the alphabet. For example:

1 => a
2 => b
3 => c
4 => d
...
27 => za
28 => zb
...
52 => zz
...
53 => zza
54 => zzb

We don’t expect to go beyond 80. Reason for converting 27 to za and so on is we need to sort based on a sort key like "10001020_**d**_10001040_10002000"

If we leave the second sort as the integer equivalent, the sort does not work as expected. Example:

"10001020_**1**_10001040_10002000"
"10001020_**10**_10001040_10002000"
"10001020_**12**_10001040_10002000"

I found this, but this ask is a little different:
Convert integer into its character equivalent, where 0 => a, 1 => b, etc

If this is not possible, we may just use an enum.

Thanks.