2, 3, 5, 8, 13, ?, 34

Correct answer: 21

Explanation:

Each term after the first two is the sum of the previous two terms (a Fibonacci-like pattern).

• Compute the missing term: 8 + 13 = 21.

• Verify the next term: 13 + 21 = 34, which matches the given following term.

Therefore the missing number is 21.