Gapplet

A few standard encodings enabling detection of a single error.

Input string s, 
consisting of capital letters and digits only,  
e.g., "ABC45E7". 		</COMMENT>
 
 
Doubling of characters of s 
 </COMMENT> </COMMENT>
Parity check added after each 7-th character of s 
 </COMMENT> </COMMENT>
Weighted parity check as in ISBN 
 </COMMENT> </COMMENT>