Closed form for $\sum_{n=2}^\infty \frac{1}{n^2\log n}$

The closed form means an expression containing only elementary functions. For your case no such a form exists. For more informations read these links:

http://www.frm.utn.edu.ar/analisisdsys/MATERIAL/Funcion_Gamma.pdf

http://en.wikipedia.org/wiki/Hölder%27s_theorem

http://en.wikipedia.org/wiki/Gamma_function#19th-20th_centuries:_characterizing_the_gamma_function

http://divizio.perso.math.cnrs.fr/PREPRINTS/16-JourneeAnnuelleSMF/difftransc.pdf

http://www.tandfonline.com/doi/abs/10.1080/17476930903394788?journalCode=gcov20

Some background are needed for your understanding and good luck with these referrences.