The CAS Registry Mumber 109635-68-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,6,3 and 5 respectively; the second part has 2 digits, 6 and 8 respectively. Calculate Digit Verification of CAS Registry Number 109635-68: (8*1)+(7*0)+(6*9)+(5*6)+(4*3)+(3*5)+(2*6)+(1*8)=139 139 % 10 = 9 So 109635-68-9 is a valid CAS Registry Number.