The CAS Registry Mumber 138973-20-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,8,9,7 and 3 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 138973-20: (8*1)+(7*3)+(6*8)+(5*9)+(4*7)+(3*3)+(2*2)+(1*0)=163 163 % 10 = 3 So 138973-20-3 is a valid CAS Registry Number.