The CAS Registry Mumber 1426-81-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,4,2 and 6 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1426-81: (6*1)+(5*4)+(4*2)+(3*6)+(2*8)+(1*1)=69 69 % 10 = 9 So 1426-81-9 is a valid CAS Registry Number.