The CAS Registry Mumber 74186-80-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,1,8 and 6 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 74186-80: (7*7)+(6*4)+(5*1)+(4*8)+(3*6)+(2*8)+(1*0)=144 144 % 10 = 4 So 74186-80-4 is a valid CAS Registry Number.