[seqfan] Re: A002955: rooted trimmed trees

[Joerg Arndt]

* Neil Sloane <njasloane at gmail.com> [Mar 03. 2015 15:56]:
> JJ, I see you used the word "unordered" in your edit of A002955.  Did you
> mean to say "unlabeled"?

Edited name:
  Number of (unordered, unlabeled) rooted trimmed trees with n nodes.

Ordered vs. unordered (the usual confusing thing):
For (all) trees, "unordered" is A000081, and "ordered" is A000108.
Cf. compositions ("unordered") and partitions ("ordered").
So "ordered" things are presented unordered,
and "unordered" things are presented ordered.

> 
> And I don't understand the phrase "pre-order walk"! Could you explain?

See
  https://en.wikipedia.org/wiki/Tree_traversal
or
  https://de.wikipedia.org/wiki/Bin%C3%A4rbaum#Traversierung
for tze Tscherman Wersion, jawoll!


Best regards,  jj

P.S.:
should a serious arbologist lurk, please see
  https://oeis.org/draft/A073075

> 
> Best regards
> Neil
> 
> [...]