The CAS Registry Mumber 125535-57-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,5,5,3 and 5 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 125535-57: (8*1)+(7*2)+(6*5)+(5*5)+(4*3)+(3*5)+(2*5)+(1*7)=121 121 % 10 = 1 So 125535-57-1 is a valid CAS Registry Number.