1Divide by 4:323 ÷ 4 = 80 remainder 3 (4×80+3=323 ✓)
2Rewrite:i323 = i4×80+3 = i4×80 · i3
3Apply i⁴=1:(i⁴)80 · i3 = 1 · i3 = i3
4Lookup r=3:i3 = −i
i323 = −iiᵏ = ir where r = k mod 4
Explanation
i⁰ = 1Any number to power 0 equals 1
i¹ = ii to the first power is i
i² = −1By definition: i² = −1
i³ = −ii³ = i² · i = −1 · i = −i