The CAS Registry Mumber 26728-13-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,6,7,2 and 8 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 26728-13: (7*2)+(6*6)+(5*7)+(4*2)+(3*8)+(2*1)+(1*3)=122 122 % 10 = 2 So 26728-13-2 is a valid CAS Registry Number.