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The value of i raised to the power i

Question

Compute i ii^{\,i}, where i=−1i=\sqrt{-1}.

Short answer

e−π/2≈0.208e^{-\pi/2}\approx0.208 (principal value), a real number. From Euler, i=eiπ/2i=e^{i\pi/2}, so ii=ei⋅iπ/2=e−π/2i^i=e^{i\cdot i\pi/2}=e^{-\pi/2}. Other branches i=ei(π/2+2πk)i=e^{i(\pi/2+2\pi k)} give e−π/2−2πke^{-\pi/2-2\pi k}.

Adapted from Zhou, A Practical Guide to Quantitative Finance Interviews, sec. 3.4 Important Calculus Methods, 'Taylor's series A', p.42; question and answer rewritten by SelfMadeQuant.com.

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