The CAS Registry Mumber 704-09-6 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, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 704-09: (5*7)+(4*0)+(3*4)+(2*0)+(1*9)=56 56 % 10 = 6 So 704-09-6 is a valid CAS Registry Number.