The CAS Registry Mumber 121722-81-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,1,7,2 and 2 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 121722-81: (8*1)+(7*2)+(6*1)+(5*7)+(4*2)+(3*2)+(2*8)+(1*1)=94 94 % 10 = 4 So 121722-81-4 is a valid CAS Registry Number.