What is wrong with this sequence?

I was given this code to figure out what is wrong with it, but cannot figure it out.

if true
  % code
  % Evaluate a sequence 
  % x_i = 4 * x_i-1 + 2 * x_i - 2
  x = zeros(1,30);
  x(1) = 10;
  x(2) = 20;
  for k = 1:length(x);
      x(k) = 2.*x(k-2)-3.*x(k-1);
  end
end

[Cedric]

What happens when k is equal to 1 or 2 ?

Answer 1

[Azzi Abdelmalek]

When k=1, k-2 is negative, and k-1 is equal to zero