The CAS Registry Mumber 138640-11-6 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 1 respectively. Calculate Digit Verification of CAS Registry Number 138640-11: (8*1)+(7*3)+(6*8)+(5*6)+(4*4)+(3*0)+(2*1)+(1*1)=126 126 % 10 = 6 So 138640-11-6 is a valid CAS Registry Number.