The CAS Registry Mumber 87673-84-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,6,7 and 3 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 87673-84: (7*8)+(6*7)+(5*6)+(4*7)+(3*3)+(2*8)+(1*4)=185 185 % 10 = 5 So 87673-84-5 is a valid CAS Registry Number.