The CAS Registry Mumber 73535-71-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,5,3 and 5 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 73535-71: (7*7)+(6*3)+(5*5)+(4*3)+(3*5)+(2*7)+(1*1)=134 134 % 10 = 4 So 73535-71-4 is a valid CAS Registry Number.