The CAS Registry Mumber 171881-26-8 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, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 171881-26: (8*1)+(7*7)+(6*1)+(5*8)+(4*8)+(3*1)+(2*2)+(1*6)=148 148 % 10 = 8 So 171881-26-8 is a valid CAS Registry Number.