The CAS Registry Mumber 2279-99-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,2,7 and 9 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 2279-99: (6*2)+(5*2)+(4*7)+(3*9)+(2*9)+(1*9)=104 104 % 10 = 4 So 2279-99-4 is a valid CAS Registry Number.