The CAS Registry Mumber 2267-21-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,2,6 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 2267-21: (6*2)+(5*2)+(4*6)+(3*7)+(2*2)+(1*1)=72 72 % 10 = 2 So 2267-21-2 is a valid CAS Registry Number.