The CAS Registry Mumber 5628-57-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,6,2 and 8 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 5628-57: (6*5)+(5*6)+(4*2)+(3*8)+(2*5)+(1*7)=109 109 % 10 = 9 So 5628-57-9 is a valid CAS Registry Number.