The CAS Registry Mumber 28303-81-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,8,3,0 and 3 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 28303-81: (7*2)+(6*8)+(5*3)+(4*0)+(3*3)+(2*8)+(1*1)=103 103 % 10 = 3 So 28303-81-3 is a valid CAS Registry Number.