(In reply to
re: Solution (spoiler) by Charlie)
When Wolfram Alpha is asked to evaluate
sum sin(k*x) / k^3,k=1 to infinity
it produces
1/2 i (Li_3(e^(i x))  Li_3(e^(i x)))
When it's asked to
plot 1/2 i (Li_3(e^(i x))  Li_3(e^(i x))), x=0 to 400
the graph seems to vary only between 1 and 1.
It seems to reach a local maximum of 1 at about 4003.7, for example, when plotting between x=4002 and 4005.

Posted by Charlie
on 20181031 11:56:13 