1 + 2 + 4 + 8 + · · ·
...that although the series 1 + 2 + 4 + 8 + · · · is ordinarily said to diverge to infinity, there is at least one generally useful method that gives its sum as −1?
...that although the <a href="./Series_(mathematics)" id="mwA-8" rel="mw:WikiLink" title="Series (mathematics)">series</a> <b id="mwA_A"><a class="mw-redirect" href="./1_+_2_+_4_+_8_+_·_·_·" id="mwA_E" rel="mw:WikiLink" title="1 + 2 + 4 + 8 + · · ·">1 + 2 + 4 + 8 + · · ·</a></b> is ordinarily said to <a href="./Divergent_series" id="mwA_I" rel="mw:WikiLink" title="Divergent series">diverge</a> to <a href="./Infinity" id="mwA_M" rel="mw:WikiLink" title="Infinity">infinity</a>, there is at least one generally useful method that gives its sum as <a class="mw-redirect" href="./Negative_one" id="mwA_Q" rel="mw:WikiLink" title="Negative one">−1</a>?