Mathematics, formulas, and algorithms have never been my strong suit, but why is this considered random if you are specifically looking for only 2/4 combinations after a set of two coin flips, without considering the other two combinations? Heads-Tails and Tails-Heads are ok, while Heads-Heads and Tails-Tails aren't. Randomness should allow all possible combinations, it's just that humans can't generate it.