The CAS Registry Mumber 728-70-1 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,2 and 8 respectively; the second part has 2 digits, 7 and 0 respectively. Calculate Digit Verification of CAS Registry Number 728-70: (5*7)+(4*2)+(3*8)+(2*7)+(1*0)=81 81 % 10 = 1 So 728-70-1 is a valid CAS Registry Number.