The CAS Registry Mumber 80170-91-8 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 0 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 80170-91: (7*8)+(6*0)+(5*1)+(4*7)+(3*0)+(2*9)+(1*1)=108 108 % 10 = 8 So 80170-91-8 is a valid CAS Registry Number.