The CAS Registry Mumber 123539-38-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,3,5,3 and 9 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 123539-38: (8*1)+(7*2)+(6*3)+(5*5)+(4*3)+(3*9)+(2*3)+(1*8)=118 118 % 10 = 8 So 123539-38-8 is a valid CAS Registry Number.