Hi Gerhard,

Thanks for pointing us to that info and the wikipedia link. We didn't know the infinite sum for $\frac{1}{k^3}$ had a special name.

The sum has been known for a long time, but as far as we know there is still no solution of it in terms of other known numbers, as there is for

  \[ \sum _{k=1}^\infty \frac{1}{k^2} = \frac{\pi ^2}{6}. \]    

Best wishes,
The Plus Team