The CAS Registry Mumber 181940-43-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,1,9,4 and 0 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 181940-43: (8*1)+(7*8)+(6*1)+(5*9)+(4*4)+(3*0)+(2*4)+(1*3)=142 142 % 10 = 2 So 181940-43-2 is a valid CAS Registry Number.