Is this an intellectual challenge? Because otherwise, use reverse().

I guess you could do something like this for INT: -

DECLARE @number INT = 500;

SELECT (SELECT N

FROM (SELECT TOP (LEN(@number))

SUBSTRING(CAST(@number AS VARCHAR(19)),N,1)

FROM (VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),

(10),(11),(12),(13),(14),(15),(16),(17),

(18),(19))a(N)

WHERE N <= (LEN(@number))

ORDER BY N DESC) b(N)

FOR XML PATH(''), TYPE).value('.', 'VARCHAR(19)');

Returns : - 005 for 500.