The CAS Registry Mumber 108098-05-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,0,9 and 8 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 108098-05: (8*1)+(7*0)+(6*8)+(5*0)+(4*9)+(3*8)+(2*0)+(1*5)=121 121 % 10 = 1 So 108098-05-1 is a valid CAS Registry Number.