Từ tập <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mstyle" id="MJXp-Span-2"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-3">A</span><span class="MJXp-mo" id="MJXp-Span-4" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mo" id="MJXp-Span-5" style="margin-left: 0em; margin-right: 0em;">{</span><span class="MJXp-mn" id="MJXp-Span-6">1</span><span class="MJXp-mo" id="MJXp-Span-7" style="margin-left: 0em; margin-right: 0.222em;">;</span><span class="MJXp-mn" id="MJXp-Span-8">2</span><span class="MJXp-mo" id="MJXp-Span-9" style="margin-left: 0em; margin-right: 0.222em;">;</span><span class="MJXp-mn" id="MJXp-Span-10">3</span><span class="MJXp-mo" id="MJXp-Span-11" style="margin-left: 0em; margin-right: 0.222em;">;</span><span class="MJXp-mn" id="MJXp-Span-12">4</span><span class="MJXp-mo" id="MJXp-Span-13" style="margin-left: 0em; margin-right: 0.222em;">;</span><span class="MJXp-mn" id="MJXp-Span-14">5</span><span class="MJXp-mo" id="MJXp-Span-15" style="margin-left: 0em; margin-right: 0em;">}</span></span></span></span><script type="math/tex" id="MathJax-Element-1">\Large A=\{1 ; 2 ; 3 ; 4 ; 5\}</script> có thể lập được bao nhiêu số t