The CAS Registry Mumber 28398-68-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,8,3,9 and 8 respectively; the second part has 2 digits, 6 and 8 respectively. Calculate Digit Verification of CAS Registry Number 28398-68: (7*2)+(6*8)+(5*3)+(4*9)+(3*8)+(2*6)+(1*8)=157 157 % 10 = 7 So 28398-68-7 is a valid CAS Registry Number.