Condensed formulae of butane, C<sub>4</sub>H<sub>10</sub>.
<a href="//commons.wikimedia.org/wiki/User:Benjah-bmm27" title="User:Benjah-bmm27">Ben Mills</a>
Own work  using:  <a href="https://en.wikipedia.org/wiki/ChemDraw" class="extiw" title="w:ChemDraw">ChemDraw</a>