The CAS Registry Mumber 108440-28-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,4,4 and 0 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 108440-28: (8*1)+(7*0)+(6*8)+(5*4)+(4*4)+(3*0)+(2*2)+(1*8)=104 104 % 10 = 4 So 108440-28-4 is a valid CAS Registry Number.