The CAS Registry Mumber 109138-05-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,1,3 and 8 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 109138-05: (8*1)+(7*0)+(6*9)+(5*1)+(4*3)+(3*8)+(2*0)+(1*5)=108 108 % 10 = 8 So 109138-05-8 is a valid CAS Registry Number.