The CAS Registry Mumber 321172-23-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,2,1,1,7 and 2 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 321172-23: (8*3)+(7*2)+(6*1)+(5*1)+(4*7)+(3*2)+(2*2)+(1*3)=90 90 % 10 = 0 So 321172-23-0 is a valid CAS Registry Number.