Where does the seven come from?

Here’s a plot of exp(6it)/2 + exp(20it)/3: Notice that the plot has 7-fold symmetry.

You might expect 6-fold symmetry from looking at the equation.

Where did the 7 come from? I produced the plot using the code from this post, changing the line defining the function to plot to def f(t): return exp(6j*t)/2 + exp(20j*t)/3 You can find the solution in Eliot’s comment in this Twitter thread.

Related links Daily exponential sum Mystery curve.

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