The CAS Registry Mumber 121671-69-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,1,6,7 and 1 respectively; the second part has 2 digits, 6 and 9 respectively. Calculate Digit Verification of CAS Registry Number 121671-69: (8*1)+(7*2)+(6*1)+(5*6)+(4*7)+(3*1)+(2*6)+(1*9)=110 110 % 10 = 0 So 121671-69-0 is a valid CAS Registry Number.