The CAS Registry Mumber 99135-16-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,1,3 and 5 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 99135-16: (7*9)+(6*9)+(5*1)+(4*3)+(3*5)+(2*1)+(1*6)=157 157 % 10 = 7 So 99135-16-7 is a valid CAS Registry Number.