MathNet 2020 — Math Olympiad Vault — Part 01 Question 113

Suppose set $X = \{1, 2, \dots, 20\}$. $A$ is a subset of $X$. The number of the elements of $A$ is at least $2$ and all the elements of $A$ can be arranged as consecutive positive integers. Then the number of such set $A$ is ______.