The CAS Registry Mumber 2736-28-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,7,3 and 6 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 2736-28: (6*2)+(5*7)+(4*3)+(3*6)+(2*2)+(1*8)=89 89 % 10 = 9 So 2736-28-9 is a valid CAS Registry Number.