uses System.Classes, System.SysUtils;

var
  Numbers: TArray<Integer>;
  Writer: TBinaryWriter;
  Number: Integer;
begin
  Numbers := [2, 5, 7];

  //arrays are not streamed natively:
  //the count and the values by hand
  Writer := TBinaryWriter.Create(
    'data.bin', False);
  try
    Writer.Write(Length(Numbers));
    for Number in Numbers do
      Writer.Write(Number);
  finally
    Writer.Free;
  end;

  WriteLn('data written to file');
end.