The CAS Registry Mumber 6209-72-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,2,0 and 9 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 6209-72: (6*6)+(5*2)+(4*0)+(3*9)+(2*7)+(1*2)=89 89 % 10 = 9 So 6209-72-9 is a valid CAS Registry Number.