The CAS Registry Mumber 128855-59-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,8,5 and 5 respectively; the second part has 2 digits, 5 and 9 respectively. Calculate Digit Verification of CAS Registry Number 128855-59: (8*1)+(7*2)+(6*8)+(5*8)+(4*5)+(3*5)+(2*5)+(1*9)=164 164 % 10 = 4 So 128855-59-4 is a valid CAS Registry Number.