Find the next number in the series:
2, 6, 12, 20, ?

Let's investigate the differences between consecutive terms:
* $6-2=4$
* $12-6=6$
* $20-12=8$

The differences sequence is an arithmetic series increasing by $2$ each time ($+4,+6,+8$). Thus, the next difference added to the sequence must be $+10$.

$$\text{Next number}=20+10=30$$

Alternatively, the pattern can be structured as $n^2+n$ where $n\in \{1,2,3,4,5\}$:

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