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Date: Sat, 19 May 2001 14:57:29 +0100
To: chemistry -A_T- ccl.net
From: Jacobo Cruces Colado <qocruces.,at,.usc.es>
Subject: CAS Registry Numbers algorithm
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Dear all:

Searching the archives of CHMINF-L&$at$&LISTSERV.INDIANA.EDU (URL is 
http://listserv.indiana.edu/archives/chminf-l.html), I found out the 
algorithm used to generate the checksum number of every CAS RN. Since it 
could be of interest for some people in the list, I will reproduce the text 
here (thanks to the original sender, Gary Wiggins; I hope not to break any 
rule by reproducing this and giving the source):

         ALGORITHM: The last digit is a checksum digit of the unit integer of
the summed products of multiplying the left-next-most integer by 1, followed by
multiplying the left-next-most integer by 2, etc.

         e.g.'s:

                 Acetone: RN= 67-64-1

         1X4 + 2X6 + 3X7 + 4X6 = 61, and 1 is the checksum digit of RN=67-64-1.

                 Butane: RN= 106-97-8
         1X7 + 2X9 + 3X6 + 4X0 + 5X1 = 48, and 8 is the checksum digit of 
RN=106-97-8

However, other people has pointed out this algorithm to be defective: due 
to our decimal notation system, the same checksum number can be obtained 
for a transposed number.

Comments??