The CAS Registry Mumber 169121-41-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,9,1,2 and 1 respectively; the second part has 2 digits, 4 and 1 respectively. Calculate Digit Verification of CAS Registry Number 169121-41: (8*1)+(7*6)+(6*9)+(5*1)+(4*2)+(3*1)+(2*4)+(1*1)=129 129 % 10 = 9 So 169121-41-9 is a valid CAS Registry Number.