The CAS Registry Mumber 110604-55-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,0,6,0 and 4 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 110604-55: (8*1)+(7*1)+(6*0)+(5*6)+(4*0)+(3*4)+(2*5)+(1*5)=72 72 % 10 = 2 So 110604-55-2 is a valid CAS Registry Number.