The CAS Registry Mumber 1616-20-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,1 and 6 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1616-20: (6*1)+(5*6)+(4*1)+(3*6)+(2*2)+(1*0)=62 62 % 10 = 2 So 1616-20-2 is a valid CAS Registry Number.