The CAS Registry Mumber 118684-21-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,8,6,8 and 4 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 118684-21: (8*1)+(7*1)+(6*8)+(5*6)+(4*8)+(3*4)+(2*2)+(1*1)=142 142 % 10 = 2 So 118684-21-2 is a valid CAS Registry Number.