The CAS Registry Mumber 726666-27-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 7,2,6,6,6 and 6 respectively; the second part has 2 digits, 2 and 7 respectively. Calculate Digit Verification of CAS Registry Number 726666-27: (8*7)+(7*2)+(6*6)+(5*6)+(4*6)+(3*6)+(2*2)+(1*7)=189 189 % 10 = 9 So 726666-27-9 is a valid CAS Registry Number.