Answer: What Comes Next? #439

The answer is B: 29.

The rule

Each number is the two numbers before it added together. 1 + 3 = 4, 3 + 4 = 7, and so on. The famous Fibonacci sequence works like this, starting 1, 1, 2, 3, 5, 8.

The pattern as Python code

Here is a tiny Python program that follows the same rule. Type it into IDLE and run it to print the whole pattern, including the answer.

a, b = 1, 3
for step in range(7):
    print(a)
    a, b = b, a + b

When you run it, Python prints:

1
3
4
7
11
18
29