��构体。很多同分异构体有相似的性质。</div>
<div>本题要求n烷的同分异构体个数。例如，丁烷（四烷？）有两个：正丁烷，异丁烷。</div>
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<p></p></div></div></div></div><div class="row"><div class="column"><h4 class="ui top attached block header">输入格式</h4><div class="ui bottom attached segment font-content"><div style="position: relative; overflow: hidden;"><div class=content><div>第一行：n，含义见题意。</div>
