The CAS Registry Mumber 74266-38-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,2,6 and 6 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 74266-38: (7*7)+(6*4)+(5*2)+(4*6)+(3*6)+(2*3)+(1*8)=139 139 % 10 = 9 So 74266-38-9 is a valid CAS Registry Number.