The CAS Registry Mumber 128457-99-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,4,5 and 7 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 128457-99: (8*1)+(7*2)+(6*8)+(5*4)+(4*5)+(3*7)+(2*9)+(1*9)=158 158 % 10 = 8 So 128457-99-8 is a valid CAS Registry Number.