+A number. The prefixes 0o and 0O (``zero oh'') force interpretation
+in octal radix; the prefixes 0t and 0T force interpretation in
+decimal radix; the prefixes 0x and 0X force interpretation in
+hexadecimal radix. Thus 0o20 = 0t16 = 0x10 = sixteen.
+If no prefix appears, then the
+.I default\ radix
+is used; see the $d command. The default radix is initially hexadecimal.
+The hexadecimal digits are 0123456789abcdefABCDEF with the obvious
+values. Note that a hexadecimal number whose most significant
+digit would otherwise be an alphabetic character must have a 0x
+(or 0X) prefix (or a leading zero if the default radix is hexadecimal).