The CAS Registry Mumber 133213-20-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,3,2,1 and 3 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 133213-20: (8*1)+(7*3)+(6*3)+(5*2)+(4*1)+(3*3)+(2*2)+(1*0)=74 74 % 10 = 4 So 133213-20-4 is a valid CAS Registry Number.