The CAS Registry Mumber 129221-24-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,9,2,2 and 1 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 129221-24: (8*1)+(7*2)+(6*9)+(5*2)+(4*2)+(3*1)+(2*2)+(1*4)=105 105 % 10 = 5 So 129221-24-5 is a valid CAS Registry Number.