The CAS Registry Mumber 133380-81-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,3,3,8 and 0 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 133380-81: (8*1)+(7*3)+(6*3)+(5*3)+(4*8)+(3*0)+(2*8)+(1*1)=111 111 % 10 = 1 So 133380-81-1 is a valid CAS Registry Number.