The CAS Registry Mumber 111981-16-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,1,9,8 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 111981-16: (8*1)+(7*1)+(6*1)+(5*9)+(4*8)+(3*1)+(2*1)+(1*6)=109 109 % 10 = 9 So 111981-16-9 is a valid CAS Registry Number.