Context-free grammar for the language ${a^{n} b^{2n+1} c^{n} a^{n-1} mid n ge 2}$

I have been trying to find a context-free grammar for the language ${a^{n} b^{2n+1} c^{n} a^{n-1} mid n ge 2}$ for some time, but I cannot get it done. Any ideas?