The CAS Registry Mumber 133728-38-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,3,7,2 and 8 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 133728-38: (8*1)+(7*3)+(6*3)+(5*7)+(4*2)+(3*8)+(2*3)+(1*8)=128 128 % 10 = 8 So 133728-38-8 is a valid CAS Registry Number.