[pdurrant]

Originally Posted by pdurrant

What is the next number in this sequence?

1
11
21
1211
111221
312211
13112221

The next number is:

Spoiler:

1113213211

It might be clearer if I wrote the numbers in a slightly different way:

1
11
21
12 11
11 12 21
31 22 11
13 11 22 21
11 13 21 32 11

and even clearer (for English speakers) if I add more spaces and some commas and 's's:

1
1 1
2 1s
1 2, 1 1
1 1, 1 2, 2 1s
3 1s, 2 2s, 1 1
1 3, 1 1, 2 2s, 2 1s
1 1, 1 3, 2 1s, 3 2s, 1 1

yes - each number (after the first) is a description of the previous number:

Congratulations to those who got it.