The CAS Registry Mumber 99797-31-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,7,9 and 7 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 99797-31: (7*9)+(6*9)+(5*7)+(4*9)+(3*7)+(2*3)+(1*1)=216 216 % 10 = 6 So 99797-31-6 is a valid CAS Registry Number.