# Equation in natural number

1. ### oszust001

10
How can I show that:
$$\sum_{i=0}^{n}2^{n-i} {n+i \choose i}=2^{2^{n}}$$
for every natural numbers

2. ### AtomSeven

8
The identity is wrong, it should be

$$\sum_{i=0}^{n}2^{n-i} {n+i \choose i}=2^{2 n}$$

3. ### oszust001

10
ok my foult. so how can i solve that equation?

4. ### AtomSeven

8
Well, this
$$\sum_{i=0}^{n}2^{n-i} {n+i \choose i}=2^{2 n}$$

is an identity it is true for all $$n$$ but, if I understand correctly, you may ask for the values of $$n$$ that make
$$\sum_{i=0}^{n}2^{n-i} {n+i \choose i}=2^{2^{n}}$$
true. In this case we have the equation $$2n=2^{2^{n}}$$, and the solutions are $$n \in \lbrace 1,2 \rbrace$$.

5. ### oszust001

10
Version of AtomSeven is good.
How can I show that $$\sum_{i=0}^{n}2^{n-i} {n+i \choose i}=2^{2 n}$$
is good for every natural numbers