The CAS Registry Mumber 108417-40-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,4,1 and 7 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 108417-40: (8*1)+(7*0)+(6*8)+(5*4)+(4*1)+(3*7)+(2*4)+(1*0)=109 109 % 10 = 9 So 108417-40-9 is a valid CAS Registry Number.