The CAS Registry Mumber 18165-33-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,8,1,6 and 5 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 18165-33: (7*1)+(6*8)+(5*1)+(4*6)+(3*5)+(2*3)+(1*3)=108 108 % 10 = 8 So 18165-33-8 is a valid CAS Registry Number.