The CAS Registry Mumber 105399-09-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,3,9 and 9 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 105399-09: (8*1)+(7*0)+(6*5)+(5*3)+(4*9)+(3*9)+(2*0)+(1*9)=125 125 % 10 = 5 So 105399-09-5 is a valid CAS Registry Number.