The CAS Registry Mumber 2440-35-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,4,4 and 0 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 2440-35: (6*2)+(5*4)+(4*4)+(3*0)+(2*3)+(1*5)=59 59 % 10 = 9 So 2440-35-9 is a valid CAS Registry Number.