Recently, I faced an interesting challenge with a valued client. In their system, a user could either choose to have a specific identifier consist of either numbers or alphabet letters. In both cases, the identifiers are unique and sequential. With numbers, the case is simple as the sequence is the expected: 1, 2, 3 … 10, 11 … n. With the alphabet numeric system, letters represent numerics values as follows: A (1), B(2) … Z(26) .. AA(27) … n. This sort of alphabetical numeric system is called Hexavigesimal, with a base of 26.

The following is the implementation in both Javascript (with a sample fiddle) and C#.