The CAS Registry Mumber 103811-55-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,3,8,1 and 1 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 103811-55: (8*1)+(7*0)+(6*3)+(5*8)+(4*1)+(3*1)+(2*5)+(1*5)=88 88 % 10 = 8 So 103811-55-8 is a valid CAS Registry Number.