The CAS Registry Mumber 81066-63-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,0,6 and 6 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 81066-63: (7*8)+(6*1)+(5*0)+(4*6)+(3*6)+(2*6)+(1*3)=119 119 % 10 = 9 So 81066-63-9 is a valid CAS Registry Number.