(a^b)^c--->a^(b*c)

I am sorry that I can't explain it enough.
I understood that in general (a^b)^b is not equal to a^(b*c). 
I want to collect "%i*c" from the formula.
But I can't use "collectterms".
Please,let me know how to convert it.

%e^(%i*c*n-%i*c)-->%e^(%i*c*(n-1))

 
(%i4) declare(n, integer)$ 
(%i5) exp(%i*c)^n/exp(%i*c);
(%o5) %e^(%i*c*n-%i*c)
(%i6)collectterms(%,%i,c);
(%o6) %e^(%i*c*n-%i*c)

%i*c*n-%i*c;
collectterms(%,c,%i);
(%o8) %i*c*(n-1)