The CAS Registry Mumber 11-23-4 includes 5 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 2 digits, 1 and 1 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 11-23: (4*1)+(3*1)+(2*2)+(1*3)=14 14 % 10 = 4 So 11-23-4 is a valid CAS Registry Number.