The CAS Registry Mumber 2033-43-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,0,3 and 3 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 2033-43: (6*2)+(5*0)+(4*3)+(3*3)+(2*4)+(1*3)=44 44 % 10 = 4 So 2033-43-4 is a valid CAS Registry Number.