what's the next number?

Question

WHAT'S THE NEXT NUMBER?
IF YOU FIND OUT THE ANSWER, THEN EXPLAIN WHY?
IT COULD BE MATH PROBLEM OR PATTERN.

1 11 21 1211 3112 211213 312213 _____

Answer 1

read: 1 number 1 ==> 11
read: 2 number 1 ==> 21
read: 1 number 2, 1 number 1, ==> 1211
read: 3 number 1, 1 number 2, ==> 3112
read: 2 number 1, 1 number 2, 1 number 3, ==> 211213
read: 3 number 1, 2 number 2, 1 number 1 ==> 312213

the next number is read like this:
2 number 1, 2 number 2, 2 number 3

so the next number is 212223

Answer 2

It's a slight variation on the classic sequence in which you read the numbers straight across:

1 = "one 1"
11 = "two 1s"
21 = "one 2, one 1"
1211 = "one 1, one 2, two 1"
111221 = "three 1s, two 2s, one 1"
312211 = "one 3, one 1, two 2s, two 1s"
13112211 = etc.

But you read all the ones first, then the twos, then the threes, etc.