Find the dissimilar number in the given series:
$2,6,24,120,540$

Let's analyze the pattern of the given series:
* $2\times 3=6$
* $6\times 4=24$
* $24\times 5=120$
* $120\times 6=720$

According to the pattern, the next term should be $720$ instead of $540$. Therefore, $540$ is the dissimilar number.