The CAS Registry Mumber 6397-16-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,3,9 and 7 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 6397-16: (6*6)+(5*3)+(4*9)+(3*7)+(2*1)+(1*6)=116 116 % 10 = 6 So 6397-16-6 is a valid CAS Registry Number.