The CAS Registry Mumber 171001-66-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,1,0,0 and 1 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 171001-66: (8*1)+(7*7)+(6*1)+(5*0)+(4*0)+(3*1)+(2*6)+(1*6)=84 84 % 10 = 4 So 171001-66-4 is a valid CAS Registry Number.