The CAS Registry Mumber 128017-49-2 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 9 respectively. Calculate Digit Verification of CAS Registry Number 128017-49: (8*1)+(7*2)+(6*8)+(5*0)+(4*1)+(3*7)+(2*4)+(1*9)=112 112 % 10 = 2 So 128017-49-2 is a valid CAS Registry Number.