The CAS Registry Mumber 4383-81-7 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,3,8 and 3 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 4383-81: (6*4)+(5*3)+(4*8)+(3*3)+(2*8)+(1*1)=97 97 % 10 = 7 So 4383-81-7 is a valid CAS Registry Number.