The CAS Registry Mumber 1873-71-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,7 and 3 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1873-71: (6*1)+(5*8)+(4*7)+(3*3)+(2*7)+(1*1)=98 98 % 10 = 8 So 1873-71-8 is a valid CAS Registry Number.