The CAS Registry Mumber 171881-35-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,1,8,8 and 1 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 171881-35: (8*1)+(7*7)+(6*1)+(5*8)+(4*8)+(3*1)+(2*3)+(1*5)=149 149 % 10 = 9 So 171881-35-9 is a valid CAS Registry Number.