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It is possible to get 6 heads in a row. With every flip, no matter what the previous flip's result was, the probability of getting either a heads or tails stays the same. If you landed on tails previously, you can still either get heads or tails and vice versa. With the interactive set to 256 coins being flipped, the average we got was 6-10 heads in a row and sometimes we landed on 8 so we think the number that the last one standing would've been 8.