The CAS Registry Mumber 142181-81-5 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 1 respectively. Calculate Digit Verification of CAS Registry Number 142181-81: (8*1)+(7*4)+(6*2)+(5*1)+(4*8)+(3*1)+(2*8)+(1*1)=105 105 % 10 = 5 So 142181-81-5 is a valid CAS Registry Number.