The CAS Registry Mumber 80171-09-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,1,7 and 1 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 80171-09: (7*8)+(6*0)+(5*1)+(4*7)+(3*1)+(2*0)+(1*9)=101 101 % 10 = 1 So 80171-09-1 is a valid CAS Registry Number.