I would appreciate if somebody could help me with the following problem
Q: Seeking a combinatorial proof $(\binom{n}{k}=\frac{n!}{k! (n-k)!} )$
$$\sum _{k=0}^n (n-2 k)^3 \binom{n}{k}=0$$
I would appreciate if somebody could help me with the following problem
Q: Seeking a combinatorial proof $(\binom{n}{k}=\frac{n!}{k! (n-k)!} )$
$$\sum _{k=0}^n (n-2 k)^3 \binom{n}{k}=0$$
$$ 2\sum _{k=0}^n (n-2 k)^3 \binom{n}{k}= \sum _{p+q=n} \left[ (n-2 p)^3 \binom{n}{p}+(n-2 q)^3 \binom{n}{q} \right] \\ =\sum _{p+q=n} \left[(n-2 p)^3 \binom{n}{p}+(2p-n)^3 \binom{n}{p} \right] \\ =0 $$