The CAS Registry Mumber 66435-38-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,6,4,3 and 5 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 66435-38: (7*6)+(6*6)+(5*4)+(4*3)+(3*5)+(2*3)+(1*8)=139 139 % 10 = 9 So 66435-38-9 is a valid CAS Registry Number.