The CAS Registry Mumber 138640-18-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,8,6,4 and 0 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 138640-18: (8*1)+(7*3)+(6*8)+(5*6)+(4*4)+(3*0)+(2*1)+(1*8)=133 133 % 10 = 3 So 138640-18-3 is a valid CAS Registry Number.