The CAS Registry Mumber 121331-24-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,1,3,3 and 1 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 121331-24: (8*1)+(7*2)+(6*1)+(5*3)+(4*3)+(3*1)+(2*2)+(1*4)=66 66 % 10 = 6 So 121331-24-6 is a valid CAS Registry Number.