The CAS Registry Mumber 17866-57-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,7,8,6 and 6 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 17866-57: (7*1)+(6*7)+(5*8)+(4*6)+(3*6)+(2*5)+(1*7)=148 148 % 10 = 8 So 17866-57-8 is a valid CAS Registry Number.