The CAS Registry Mumber 118683-55-9 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 3 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 118683-55: (8*1)+(7*1)+(6*8)+(5*6)+(4*8)+(3*3)+(2*5)+(1*5)=149 149 % 10 = 9 So 118683-55-9 is a valid CAS Registry Number.