The CAS Registry Mumber 128253-54-3 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 4 respectively. Calculate Digit Verification of CAS Registry Number 128253-54: (8*1)+(7*2)+(6*8)+(5*2)+(4*5)+(3*3)+(2*5)+(1*4)=123 123 % 10 = 3 So 128253-54-3 is a valid CAS Registry Number.