The CAS Registry Mumber 873-98-3 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 8,7 and 3 respectively; the second part has 2 digits, 9 and 8 respectively. Calculate Digit Verification of CAS Registry Number 873-98: (5*8)+(4*7)+(3*3)+(2*9)+(1*8)=103 103 % 10 = 3 So 873-98-3 is a valid CAS Registry Number.