You may use [`QuotientRemainder`](https://reference.wolfram.com/language/ref/QuotientRemainder.html) with [`FromLetterNumber`](https://reference.wolfram.com/language/ref/FromLetterNumber.html) and a bit of recursion.

    ClearAll[baseAlphabetForm]
    SetAttributes[baseAlphabetForm, Listable];
    baseAlphabetForm[expr_Integer?NonNegative] :=
      If[
      expr == 0
      , ""
      , Module[
       {q, r}
       , {q, r} = QuotientRemainder[expr, 26]
       ; If[r == 0, (q -= 1; r = 26;)]
       ; StringJoin[{baseAlphabetForm[q], ToUpperCase@FromLetterNumber[r]}]
         ]
       ]

Then 

    baseAlphabetForm[10]

>     "J"

and

    baseAlphabetForm[{7288884863, 1844844242797219}]

>     {"WOLFRAM", "MATHEMATICA"}

and

    baseAlphabetForm[Range[100]] //
     Multicolumn[#, Frame -> All, Appearance -> "Horizontal"] &

> ![Mathematica graphics](https://i.sstatic.net/1m2jH.png)

Hope this helps.