The CAS Registry Mumber 121238-05-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,1,2,3 and 8 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 121238-05: (8*1)+(7*2)+(6*1)+(5*2)+(4*3)+(3*8)+(2*0)+(1*5)=79 79 % 10 = 9 So 121238-05-9 is a valid CAS Registry Number.