MATLAB: Loop: stop if value repeats

Question

In my case this is based on

N = Number 
G = Guess
x = 1:N
R= mod(G^x,N)

if R repeats I want the calculation mod(G^x,N) to stop and tell me the steps P that it needed to to get to R again

for example if R = 1, 4 3, 2, 1 -stop, P = 4

Answer 1

N = Number; 
G = Guess;
x = 1:N;
R = nan(1, N);
found = N;
for k = 1:N
  R(k) = mod(G^x(k), N);
  if any(R(1:k-1) == R(k))
      found = k;
      break
  end
end
R = R(1:found)