Mathematical Induction And Binomial Theorem

Let $a_0, a_1, \ldots, a_{23}$ be real numbers such that

\(\left(1+\frac{2}{5} x\right)^{23}=\sum\limits_{i=0}^{23} a_i x^i\)

for every real number $x$. Let $a_r$ be the largest among the numbers $a_j$ for $0 \leq j \leq 23$. Then the value of $r$ is ____________.