Find all sets of real numbers $\{a_1,a_2,\ldots, _{1375}\}$ such that
\[2 \left( \sqrt{a_n - (n-1)}\right) \geq a_{n+1} - (n-1), \quad \forall n \in \{1,2,\ldots,1374\},\]
and
\[2 \left( \sqrt{a_{1375}-1374} \right) \geq a_1 +1.\]
1. Define \( x_n := a_n - (n-1) \). This substitution simplifies the given inequalities. The inequalities become:
   \[
   2 \left( \sqrt{x_n} \right) \geq x_{n+1} - (n-1) - (n-1) = x_{n+1}, \quad \forall n \in \{1, 2, \ldots, 1374\}
   \]
   and
   \[
   2 \left( \sqrt{x_{1375}} \right) \geq a_1 + 1 - 1374 = x_1 + 1.
   \]

2. Rearrange the first inequality:
   \[
   2 \sqrt{x_n} \geq x_{n+1}
   \]
   This implies:
   \[
   x_{n+1} \leq 2 \sqrt{x_n}
   \]

3. Rearrange the second inequality:
   \[
   2 \sqrt{x_{1375}} \geq x_1 + 1
   \]

4. Consider the sequence \( x_n \). We need to show that \( x_n = 1 \) for all \( n \). Assume \( x_n = 1 \) for all \( n \). Then:
   \[
   2 \sqrt{1} = 2 \geq 1 = x_{n+1}
   \]
   and
   \[
   2 \sqrt{1} = 2 \geq 1 + 1 = x_1 + 1
   \]
   Both inequalities hold true.

5. To prove that \( x_n = 1 \) is the only solution, consider the sum of the inequalities:
   \[
   x_n - x_{n+1} \geq (\sqrt{x_n} - 1)^2, \quad \forall n \in \{1, 2, \ldots, 1374\}
   \]
   and
   \[
   x_{1375} - x_1 \geq (\sqrt{x_{1375}} - 1)^2
   \]

6. Adding these inequalities from \( n = 1 \) to \( n = 1374 \) and including the last inequality:
   \[
   \sum_{n=1}^{1374} (x_n - x_{n+1}) + (x_{1375} - x_1) \geq \sum_{n=1}^{1374} (\sqrt{x_n} - 1)^2 + (\sqrt{x_{1375}} - 1)^2
   \]
   The left-hand side telescopes to:
   \[
   x_1 - x_{1375} + x_{1375} - x_1 = 0
   \]
   Thus:
   \[
   0 \geq \sum_{n=1}^{1375} (\sqrt{x_n} - 1)^2
   \]

7. Since each term \((\sqrt{x_n} - 1)^2 \geq 0\), the only way the sum can be zero is if each term is zero:
   \[
   (\sqrt{x_n} - 1)^2 = 0 \implies \sqrt{x_n} = 1 \implies x_n = 1
   \]

8. Therefore, \( x_n = 1 \) for all \( n \). Substituting back, we get:
   \[
   a_n - (n-1) = 1 \implies a_n = n
   \]

Conclusion:
\[
\boxed{a_n = n \text{ for all } n \in \{1, 2, \ldots, 1375\}}
\]