The CAS Registry Mumber 21443-83-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,1,4,4 and 3 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 21443-83: (7*2)+(6*1)+(5*4)+(4*4)+(3*3)+(2*8)+(1*3)=84 84 % 10 = 4 So 21443-83-4 is a valid CAS Registry Number.