The CAS Registry Mumber 1399-18-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,3,9 and 9 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 1399-18: (6*1)+(5*3)+(4*9)+(3*9)+(2*1)+(1*8)=94 94 % 10 = 4 So 1399-18-4 is a valid CAS Registry Number.