The CAS Registry Mumber 8021-84-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 8,0,2 and 1 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 8021-84: (6*8)+(5*0)+(4*2)+(3*1)+(2*8)+(1*4)=79 79 % 10 = 9 So 8021-84-9 is a valid CAS Registry Number.