The CAS Registry Mumber 19921-16-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,9,9,2 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 19921-16: (7*1)+(6*9)+(5*9)+(4*2)+(3*1)+(2*1)+(1*6)=125 125 % 10 = 5 So 19921-16-5 is a valid CAS Registry Number.