The CAS Registry Mumber 1716-57-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,1 and 6 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 1716-57: (6*1)+(5*7)+(4*1)+(3*6)+(2*5)+(1*7)=80 80 % 10 = 0 So 1716-57-0 is a valid CAS Registry Number.