The CAS Registry Mumber 2225-21-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,2,2 and 5 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 2225-21: (6*2)+(5*2)+(4*2)+(3*5)+(2*2)+(1*1)=50 50 % 10 = 0 So 2225-21-0 is a valid CAS Registry Number.