The CAS Registry Mumber 404-53-5 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,0 and 4 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 404-53: (5*4)+(4*0)+(3*4)+(2*5)+(1*3)=45 45 % 10 = 5 So 404-53-5 is a valid CAS Registry Number.