The CAS Registry Mumber 138407-34-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,8,4,0 and 7 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 138407-34: (8*1)+(7*3)+(6*8)+(5*4)+(4*0)+(3*7)+(2*3)+(1*4)=128 128 % 10 = 8 So 138407-34-8 is a valid CAS Registry Number.