The CAS Registry Mumber 18389-61-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,8,3,8 and 9 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 18389-61: (7*1)+(6*8)+(5*3)+(4*8)+(3*9)+(2*6)+(1*1)=142 142 % 10 = 2 So 18389-61-2 is a valid CAS Registry Number.