digit-char
(digit-char weight &optional radix)
Returns the character denoting weight in radix (10 by default), in upper case, or nil when the weight is not a non-negative integer below the radix. It is the inverse of digit-char-p.
(digit-char weight &optional radix)
Returns the character denoting weight in radix (10 by default), in upper case, or nil when the weight is not a non-negative integer below the radix. It is the inverse of digit-char-p.