The CAS Registry Mumber 126398-98-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,6,3,9 and 8 respectively; the second part has 2 digits, 9 and 8 respectively. Calculate Digit Verification of CAS Registry Number 126398-98: (8*1)+(7*2)+(6*6)+(5*3)+(4*9)+(3*8)+(2*9)+(1*8)=159 159 % 10 = 9 So 126398-98-9 is a valid CAS Registry Number.