The CAS Registry Mumber 566-77-8 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 5,6 and 6 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 566-77: (5*5)+(4*6)+(3*6)+(2*7)+(1*7)=88 88 % 10 = 8 So 566-77-8 is a valid CAS Registry Number.