Let \( a_0, a_1, \ldots, a_{23} \) be real numbers such that \( \left(1 + \dfrac{2}{5}x\right)^{23} = \displaystyle\sum_{i=0}^{23} a_i x^i \) for every real number \( x \). Let \( a_r \) be the largest among the numbers \( a_j \) for \( 0 \le j \le 23 \). Then the value of \( r \) is __________.
