The CAS Registry Mumber 138973-31-6 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, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 138973-31: (8*1)+(7*3)+(6*8)+(5*9)+(4*7)+(3*3)+(2*3)+(1*1)=166 166 % 10 = 6 So 138973-31-6 is a valid CAS Registry Number.