The CAS Registry Mumber 399-54-2 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 3,9 and 9 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 399-54: (5*3)+(4*9)+(3*9)+(2*5)+(1*4)=92 92 % 10 = 2 So 399-54-2 is a valid CAS Registry Number.