The CAS Registry Mumber 109687-41-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,6,8 and 7 respectively; the second part has 2 digits, 4 and 1 respectively. Calculate Digit Verification of CAS Registry Number 109687-41: (8*1)+(7*0)+(6*9)+(5*6)+(4*8)+(3*7)+(2*4)+(1*1)=154 154 % 10 = 4 So 109687-41-4 is a valid CAS Registry Number.