The CAS Registry Mumber 128253-52-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,2,5 and 3 respectively; the second part has 2 digits, 5 and 2 respectively. Calculate Digit Verification of CAS Registry Number 128253-52: (8*1)+(7*2)+(6*8)+(5*2)+(4*5)+(3*3)+(2*5)+(1*2)=121 121 % 10 = 1 So 128253-52-1 is a valid CAS Registry Number.