The CAS Registry Mumber 17066-71-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,0,6 and 6 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 17066-71: (7*1)+(6*7)+(5*0)+(4*6)+(3*6)+(2*7)+(1*1)=106 106 % 10 = 6 So 17066-71-6 is a valid CAS Registry Number.