The CAS Registry Mumber 25596-28-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,5,9 and 6 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 25596-28: (7*2)+(6*5)+(5*5)+(4*9)+(3*6)+(2*2)+(1*8)=135 135 % 10 = 5 So 25596-28-5 is a valid CAS Registry Number.