Question 1129474
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The number that the question asks for is  {{{2^7}}} = 128.


Each sequence is the word of 7 symbols, written using only TWO symbols H or T.


So, each position of such a 7-symbols word is the letter H or T.


And the full number of these words (= of these sequences) is  {{{2^7}}} = 128. 


It is the number the question is asking for.      <U>ANSWER</U>
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Solved.