The CAS Registry Mumber 139109-09-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,9,1,0 and 9 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 139109-09: (8*1)+(7*3)+(6*9)+(5*1)+(4*0)+(3*9)+(2*0)+(1*9)=124 124 % 10 = 4 So 139109-09-4 is a valid CAS Registry Number.