The CAS Registry Mumber 123557-88-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,3,5,5 and 7 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 123557-88: (8*1)+(7*2)+(6*3)+(5*5)+(4*5)+(3*7)+(2*8)+(1*8)=130 130 % 10 = 0 So 123557-88-0 is a valid CAS Registry Number.