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 below the radix. A weight that is not a non-negative integer signals a type-error (type UNSIGNED-BYTE), and so does a radix that is not an integer from 2 to 36 (type (INTEGER 2 36)), the weight checked first. It is the inverse of digit-char-p.