The CAS Registry Mumber 20940-04-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,0,9,4 and 0 respectively; the second part has 2 digits, 0 and 4 respectively. Calculate Digit Verification of CAS Registry Number 20940-04: (7*2)+(6*0)+(5*9)+(4*4)+(3*0)+(2*0)+(1*4)=79 79 % 10 = 9 So 20940-04-9 is a valid CAS Registry Number.