Q1321 Find the sum of the coefficients of those terms in the expansion of $$(x^{31}+x^5-1)^{2011}$$ which have an odd exponent in $x$

 

Note that $$(x^{31}+x^5-1)^{2011}=a_nx^n + a_{n-1}x^{n-1} + \cdots + a_1x + a_0$$