The CAS Registry Mumber 20831-99-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,0,8,3 and 1 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 20831-99: (7*2)+(6*0)+(5*8)+(4*3)+(3*1)+(2*9)+(1*9)=96 96 % 10 = 6 So 20831-99-6 is a valid CAS Registry Number.