The CAS Registry Mumber 211-33-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 2,1 and 1 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 211-33: (5*2)+(4*1)+(3*1)+(2*3)+(1*3)=26 26 % 10 = 6 So 211-33-6 is a valid CAS Registry Number.