# Sequence next in sequence

From Math Puzzle Wiki

This sequence guessing puzzle hides a beautiful, well known sequence.

## Puzzle

What comes next: 1, 2, 2, 1, 1, 2, 1, ....?

## Help

**Hint**

Count the number of repeating digits.

**Answer**

2

**Solution**

This is the famous Kolakoski sequence (see the wikipedia page listed below). The sequence self-encodes the run length of repeated digits. These run lengths are 1, 2, 2, 1, 1, 2, 1,...., which is the sequence again.

## Bonus

Find a sequence using the numbers 1, 2, and 3 that has the same property as the one above.

## References

Wikipedia page (contains spoilers).