The CAS Registry Mumber 25363-28-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,3,6 and 3 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 25363-28: (7*2)+(6*5)+(5*3)+(4*6)+(3*3)+(2*2)+(1*8)=104 104 % 10 = 4 So 25363-28-4 is a valid CAS Registry Number.