The CAS Registry Mumber 128017-43-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,0,1 and 7 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 128017-43: (8*1)+(7*2)+(6*8)+(5*0)+(4*1)+(3*7)+(2*4)+(1*3)=106 106 % 10 = 6 So 128017-43-6 is a valid CAS Registry Number.