The CAS Registry Mumber 84866-42-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,4,8,6 and 6 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 84866-42: (7*8)+(6*4)+(5*8)+(4*6)+(3*6)+(2*4)+(1*2)=172 172 % 10 = 2 So 84866-42-2 is a valid CAS Registry Number.