The CAS Registry Mumber 54053-43-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,4,0,5 and 3 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 54053-43: (7*5)+(6*4)+(5*0)+(4*5)+(3*3)+(2*4)+(1*3)=99 99 % 10 = 9 So 54053-43-9 is a valid CAS Registry Number.