The CAS Registry Mumber 51104-80-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,1,1,0 and 4 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 51104-80: (7*5)+(6*1)+(5*1)+(4*0)+(3*4)+(2*8)+(1*0)=74 74 % 10 = 4 So 51104-80-4 is a valid CAS Registry Number.