The CAS Registry Mumber 128397-98-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,3,9 and 7 respectively; the second part has 2 digits, 9 and 8 respectively. Calculate Digit Verification of CAS Registry Number 128397-98: (8*1)+(7*2)+(6*8)+(5*3)+(4*9)+(3*7)+(2*9)+(1*8)=168 168 % 10 = 8 So 128397-98-8 is a valid CAS Registry Number.