Let \(f(x)=\left\{\begin{array}{l}x-1, x \text { is even, } \\ 2 x, \quad x \text { is odd, }\end{array} x \in N\right.\…

Let \(f(x)=\left\{\begin{array}{l}x-1, x \text { is even, } \\ 2 x, \quad x \text { is odd, }\end{array} x \in N\right.\). If for some \(a \in N , f(f(f( a )))=21\), then \(\lim _{x \rightarrow a ^{-}}\left\{\frac{|x|^3}{ a }-\left[\frac{x}{ a }\right]\right\}\), where \([t]\) denotes the greatest integer less than or equal to \(t\), is equal to :EndFragment

[JEE Main 2024, 01 Feb (Shift 2)]