The CAS Registry Mumber 128531-18-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,5,3 and 1 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 128531-18: (8*1)+(7*2)+(6*8)+(5*5)+(4*3)+(3*1)+(2*1)+(1*8)=120 120 % 10 = 0 So 128531-18-0 is a valid CAS Registry Number.