The CAS Registry Mumber 142181-80-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,4,2,1,8 and 1 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 142181-80: (8*1)+(7*4)+(6*2)+(5*1)+(4*8)+(3*1)+(2*8)+(1*0)=104 104 % 10 = 4 So 142181-80-4 is a valid CAS Registry Number.