The CAS Registry Mumber 321172-65-0 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, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 321172-65: (8*3)+(7*2)+(6*1)+(5*1)+(4*7)+(3*2)+(2*6)+(1*5)=100 100 % 10 = 0 So 321172-65-0 is a valid CAS Registry Number.