The CAS Registry Mumber 577-99-1 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 5,7 and 7 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 577-99: (5*5)+(4*7)+(3*7)+(2*9)+(1*9)=101 101 % 10 = 1 So 577-99-1 is a valid CAS Registry Number.