The CAS Registry Mumber 17331-11-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,3,3 and 1 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 17331-11: (7*1)+(6*7)+(5*3)+(4*3)+(3*1)+(2*1)+(1*1)=82 82 % 10 = 2 So 17331-11-2 is a valid CAS Registry Number.