The CAS Registry Mumber 122128-24-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,2,1,2 and 8 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 122128-24: (8*1)+(7*2)+(6*2)+(5*1)+(4*2)+(3*8)+(2*2)+(1*4)=79 79 % 10 = 9 So 122128-24-9 is a valid CAS Registry Number.