вылетает программа

const {Enter A & B}
n=21; {Razmernost}
X:array[1..n] of real=(-1.0,-0.9,-0.8,-0.7,-0.6,-0.5,-0.4,-0.3,-0.2,-0.1,-0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0);
B:array[1..n] of real=(-3.99885,-3.97694,-3.88664,-3.73027,-3.51182,-3.23686,-2.91243,-2.54680,-2.14933,-1.73016,-1.30000,-0.86984,-0.45067,-0.05320,-0.31243,-0.63686,-0.91180,1.13027,1.28664,1.37694,1.39885);
{B eto Y}
 
var
AA:array[1..n] of real; {massiv koefficientov Ao,A1 funkcii i t.d. (korni X)}
A:array[1..n,1..n] of real; {Matrica znachenii X}
i,j,k:integer;        {Vnutrennie peremennie ciclov}
sum:real;
F:array[1..n,1..n+1] of real; {Promejutochnie znachenia F}
 
function Stepen (X:real;i:integer):real; {vozvedenie X v stepen i}
var
   m:integer;
   S:real;
begin
 s:=1/X;
 for m:=1 to j do
 S:=S*X;
 Stepen:=S;
end;
 
begin
 for i:=1 to n do
  for j:=1 to n do
  A[i,j]:=Stepen(X[i],j); {zanosim znachenia X v A}
   {Vichislenie metodom Gaussa korney yravnenia}
  for k:=1 to n do
  begin
   for j:=k to n do
   F[k,j]:=-A[k,j]/A[k,k];
  F[k,n+1]:=-B[k]/A[k,k];
   for i:=k+1 to n do
   begin
    for j:=k+1 to n do
    A[i,j]:=A[i,j]+A[i,k]*F[k,j];
   {B[i]:=B[i]+A[i,k]*F[k,n+1];}
   end;
  end;
  for i:=n downto 1 do
  begin
   for j:=n downto 2 do
   sum:=sum+F[i,j]*AA[j];
  AA[i]:=sum-F[i,n+1];
  sum:=0
  end;
for i:=0 to n-1 do
writeln('A',i,'=',AA[i+1]);
readln;
end.

function Stepen(X: real; i: integer): real; { vozvedenie X v stepen i }
var
  m: integer;
  S: real;
begin
  try
    S := 1 / X;
  except
    on e: Exception do
      ShowMessage(e.Message);
  end;
  for m := 1 to i do
    S := S * X;
  Stepen := S;
end;