### Home > MC1 > Chapter 7 > Lesson 7.2.2 > Problem7-61

7-61.

What are the next three numbers in the pattern: $1,3,7,13,21,\dots$? Describe the pattern in words.

Write down the differences between each number and the number after it.
There is a pattern in the amounts by which the numbers increase.

The difference between $1$ and $3$ is $2$, the difference between $3$ and $7$ is $4$, the difference between $7$ and $13$ is $6$, and the difference between $13$ and $21$ is $8$. The amount added follows the pattern $2$, $4$, $6$, $8$, and so on.