The CAS Registry Mumber 73353-98-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,3,5 and 3 respectively; the second part has 2 digits, 9 and 8 respectively. Calculate Digit Verification of CAS Registry Number 73353-98: (7*7)+(6*3)+(5*3)+(4*5)+(3*3)+(2*9)+(1*8)=137 137 % 10 = 7 So 73353-98-7 is a valid CAS Registry Number.