The CAS Registry Mumber 53491-28-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,4,9 and 1 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 53491-28: (7*5)+(6*3)+(5*4)+(4*9)+(3*1)+(2*2)+(1*8)=124 124 % 10 = 4 So 53491-28-4 is a valid CAS Registry Number.