n class=sampledata>650<br />
Only words of the form xyyx are palindromically equivalent to abba, where x and y are distinct letters. <br />
The English alphabet contains 26 letters, consequently there are 26*25=650  such words in total.</span></div></code></pre></div></div></div></div></div><div class="row"><div class="column"><h4 class="ui top attached block header">数据范围与提示</h4><div class="ui bottom attached segment font-content"><div style="position: relative; overflow: hidden;">
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