The CAS Registry Mumber 81109-38-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,1,0 and 9 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 81109-38: (7*8)+(6*1)+(5*1)+(4*0)+(3*9)+(2*3)+(1*8)=108 108 % 10 = 8 So 81109-38-8 is a valid CAS Registry Number.