The CAS Registry Mumber 52806-20-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,2,8,0 and 6 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 52806-20: (7*5)+(6*2)+(5*8)+(4*0)+(3*6)+(2*2)+(1*0)=109 109 % 10 = 9 So 52806-20-9 is a valid CAS Registry Number.