The CAS Registry Mumber 73871-01-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,8,7 and 1 respectively; the second part has 2 digits, 0 and 1 respectively. Calculate Digit Verification of CAS Registry Number 73871-01: (7*7)+(6*3)+(5*8)+(4*7)+(3*1)+(2*0)+(1*1)=139 139 % 10 = 9 So 73871-01-9 is a valid CAS Registry Number.