String length $\left | w \right |$ which is divided by 3 and not divided by 2 are not accepted like 3,9,15,21
$S \rightarrow aA \mid \lambda$
$A \rightarrow aB \mid \lambda$
$B \rightarrow aC \mid \lambda$
$C \rightarrow aD$
$D \rightarrow aE \mid \lambda$
$E \rightarrow aS \mid \lambda$