The CAS Registry Mumber 105399-08-4 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 8 respectively. Calculate Digit Verification of CAS Registry Number 105399-08: (8*1)+(7*0)+(6*5)+(5*3)+(4*9)+(3*9)+(2*0)+(1*8)=124 124 % 10 = 4 So 105399-08-4 is a valid CAS Registry Number.