The CAS Registry Mumber 71733-18-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,1,7,3 and 3 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 71733-18: (7*7)+(6*1)+(5*7)+(4*3)+(3*3)+(2*1)+(1*8)=121 121 % 10 = 1 So 71733-18-1 is a valid CAS Registry Number.