The CAS Registry Mumber 75421-03-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,4,2 and 1 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 75421-03: (7*7)+(6*5)+(5*4)+(4*2)+(3*1)+(2*0)+(1*3)=113 113 % 10 = 3 So 75421-03-3 is a valid CAS Registry Number.