Question: Cho dãy <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-msubsup" id="MJXp-Span-2"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-3" style="margin-right: 0.05em;">a</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-4" style="vertical-align: -0.4em;"><span class="MJXp-mn" id="MJXp-Span-5">1</span></span></span><span class="MJXp-mo" id="MJXp-Span-6" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-msubsup" id="MJXp-Span-7"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-8" style="margin-right: 0.05em;">a</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-9" style="vertical-align: -0.4em;"><span class="MJXp-mn" id="MJXp-Span-10">2</span></span></span><span class="MJXp-mo" id="MJXp-Span-11" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-msubsup" id="MJXp-Span-12"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-13" style="margin-right: 0.05em;">a</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-14" style="vertical-align: -0.4em;"><span class="MJXp-mn" id="MJXp-Span-15">3</span></span></span><span class="MJXp-mo" id="MJXp-Span-16" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-msubsup" id="MJXp-Span-17"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-18" style="margin-right: 0.05em;">a</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-19" style="vertical-align: -0.4em;"><span class="MJXp-mn" id="MJXp-Span-20">4</span></span></span></span></span><script type="math/tex" id="MathJax-Element-1">a_{1},a_{2},a_{3},a_{4}</script>, với mỗi <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-21"><span class="MJXp-msubsup" id="MJXp-Span-22"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-23" style="margin-right: 0.05em;">a</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-24" style="vertical-align: -0.4em;"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-25">i</span></span></span></span></span><script type="math/tex" id="MathJax-Element-2">a_{i}</script> chỉ nhận giá trị 0 hoặc 1. Hỏi có bao nhiêu dãy như vậy?