Answer
$j$
Work Step by Step
Since $j=\sqrt{-1}$, $j^2=-1$, $j^4=1$, we have
$$ j^{13}=j^{12}j=j$$
where we used the fact that $12=4\times 3$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.