nFor a 2-letter search word, either letter can occur in either order at any spacing, so the probability is about 33 x 33 = 1089.
nFor search words of 3 letters or more, the rule that the code-words appear with equidistant spacing makes matches much rarer.  The 3rd letter must be exactly the same distance from the 2nd as the 2nd from the 1st. N = 1089/21 = 52.