The CAS Registry Mumber 704-28-9 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,0 and 4 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 704-28: (5*7)+(4*0)+(3*4)+(2*2)+(1*8)=59 59 % 10 = 9 So 704-28-9 is a valid CAS Registry Number.