Concept:
The given sequence follows a pattern based on the product of consecutive natural numbers:
\[
a_n = n(n+1)
\]
Step 1: Verify the pattern.
\[
1 \times 2 = 2,\quad
2 \times 3 = 6,\quad
3 \times 4 = 12,\quad
4 \times 5 = 20
\]
Step 2: Apply pattern for next term.
\[
5 \times 6 = 30
\]
Step 3: Alternative observation (difference method).
\[
6 - 2 = 4,\quad
12 - 6 = 6,\quad
20 - 12 = 8
\]
Differences increase by 2, so next difference = 10:
\[
20 + 10 = 30
\]
Step 4: Conclusion.
Thus, the next number in the series is 30.