The CAS Registry Mumber 2082-20-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,0,8 and 2 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 2082-20: (6*2)+(5*0)+(4*8)+(3*2)+(2*2)+(1*0)=54 54 % 10 = 4 So 2082-20-4 is a valid CAS Registry Number.