Find the value of `sumsum_(0leiltjlen) (""^(n)C_(i)+""^(n)C_(j))`.

Explanation

To solve the problem of finding the value of the summation \( \sum_{0 \leq i < j \leq n} \left( \binom{n}{i} + \binom{n}{j} \right) \), we can break it down into manageable steps.

### Step-by-Step Solution:

1. **Understanding the Summation**:
We need to evaluate the expression \( \sum_{0 \leq i < j \leq n} \left( \binom{n}{i} + \binom{n}{j} \right) \). This can be rewritten as:
\[
\sum_{0 \leq i < j \leq n} \binom{n}{i} + \sum_{0 \leq i < j \leq n} \binom{n}{j}
...