The CAS Registry Mumber 16613-45-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,6,6,1 and 3 respectively; the second part has 2 digits, 4 and 5 respectively. Calculate Digit Verification of CAS Registry Number 16613-45: (7*1)+(6*6)+(5*6)+(4*1)+(3*3)+(2*4)+(1*5)=99 99 % 10 = 9 So 16613-45-9 is a valid CAS Registry Number.