Riddles/stuff

38

The next number is: 1312221. Each number describes the previous number.
Starting with 1, the second line describes it as 11 (one 1). Then the third line describes 11 as 21 (two 1's). Then the fourth line describes 21 as 1211 (one 2, one 1). This is the pattern.
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I am the first on earth, the second in heaven.
I appear twice in a week, though you can only see me once in a year.
What am I?