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How many pure trees of size (number of nodes) $n$ exist? Apart from having this fixed size, the trees can be arbitrary.

The sequence starts like this:

Here's the beginning of the sequence:

1 1 2 5

fefrei
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  • Have a look at this related post: http://math.stackexchange.com/questions/169155/number-of-trees-with-n-nodes?rq=1 – Axel Kemper Nov 15 '14 at 15:30
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    This is the catalan numebers, OEIS A000108 – MJD Nov 15 '14 at 16:26
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    Dear closevoters: that related post is not a duplicate (it's being asked by someone who already knows about Catalan numbers and is looking for a generalization). – Micah Nov 15 '14 at 16:31
  • Catalan numbers seems to be right - although I'm confused because the related question claims they are just for the binary trees. – fefrei Nov 15 '14 at 19:38

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