Complete the series.
$$2,6,12,20,30,42,\_\_\_\_$$

Let's analyze the consecutive differences between the numbers in the series:
* $6-2=4$
* $12-6=6$
* $20-12=8$
* $30-20=10$
* $42-30=12$

The differences form an arithmetic progression of consecutive even numbers: $4,6,8,10,12$.
Therefore, the next difference must be $14$.

$$\text{Next number}=42+14=56$$

Alternative Method:
The series follows the formula $n(n+1)$ or $n^2+n$ for consecutive integers starting from $n=1$:

* $1^2+1=2$
* $2^2+2=6$
* $3^2+3=12$
* $4^2+4=20$
* $5^2+5=30$
* $6^2+6=42$
* $7^2+7=56$