The CAS Registry Mumber 126520-66-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,6,5,2 and 0 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 126520-66: (8*1)+(7*2)+(6*6)+(5*5)+(4*2)+(3*0)+(2*6)+(1*6)=109 109 % 10 = 9 So 126520-66-9 is a valid CAS Registry Number.