The CAS Registry Mumber 71700-16-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,1,7,0 and 0 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 71700-16: (7*7)+(6*1)+(5*7)+(4*0)+(3*0)+(2*1)+(1*6)=98 98 % 10 = 8 So 71700-16-8 is a valid CAS Registry Number.