The CAS Registry Mumber 87540-73-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,5,4 and 0 respectively; the second part has 2 digits, 7 and 3 respectively. Calculate Digit Verification of CAS Registry Number 87540-73: (7*8)+(6*7)+(5*5)+(4*4)+(3*0)+(2*7)+(1*3)=156 156 % 10 = 6 So 87540-73-6 is a valid CAS Registry Number.