The CAS Registry Mumber 501-57-5 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 5,0 and 1 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 501-57: (5*5)+(4*0)+(3*1)+(2*5)+(1*7)=45 45 % 10 = 5 So 501-57-5 is a valid CAS Registry Number.