The CAS Registry Mumber 40709-80-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,0,7,0 and 9 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 40709-80: (7*4)+(6*0)+(5*7)+(4*0)+(3*9)+(2*8)+(1*0)=106 106 % 10 = 6 So 40709-80-6 is a valid CAS Registry Number.