The CAS Registry Mumber 1628-51-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,2 and 8 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1628-51: (6*1)+(5*6)+(4*2)+(3*8)+(2*5)+(1*1)=79 79 % 10 = 9 So 1628-51-9 is a valid CAS Registry Number.