The CAS Registry Mumber 2273-13-4 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 3 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 2273-13: (6*2)+(5*2)+(4*7)+(3*3)+(2*1)+(1*3)=64 64 % 10 = 4 So 2273-13-4 is a valid CAS Registry Number.