"Look and say"

What's the next element of the sequence?

The sequence presented to John Conway was: 1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, ... The secret behind it isn't any ingenious mathematical formula (Conway would have found it...) but is rather trivial: "Look at the numbers and say what's written. Then write what you just said"