The CAS Registry Mumber 998-86-7 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 9,9 and 8 respectively; the second part has 2 digits, 8 and 6 respectively. Calculate Digit Verification of CAS Registry Number 998-86: (5*9)+(4*9)+(3*8)+(2*8)+(1*6)=127 127 % 10 = 7 So 998-86-7 is a valid CAS Registry Number.