The CAS Registry Mumber 128231-11-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,2,3 and 1 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 128231-11: (8*1)+(7*2)+(6*8)+(5*2)+(4*3)+(3*1)+(2*1)+(1*1)=98 98 % 10 = 8 So 128231-11-8 is a valid CAS Registry Number.