The CAS Registry Mumber 838-53-9 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 8,3 and 8 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 838-53: (5*8)+(4*3)+(3*8)+(2*5)+(1*3)=89 89 % 10 = 9 So 838-53-9 is a valid CAS Registry Number.