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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A121320 Number of vertices in all ordered (plane) trees with n edges that are at distance two from all the leaves above them.

Table of values

n a(n)
0 0
1 0
2 1
3 2
4 6
5 18
6 59
7 203
8 724
9 2643
10 9802
11 36755
12 138935
13 528406
14 2019419
15 7748125
16 29825844
17 115132729
18 445498768
19 1727434607
20 6710501025
21 26110567532
22 101744332967
23 396983837719
24 1550777652546
25 6064476854065
26 23739056348161

List of values

[0, 0, 1, 2, 6, 18, 59, 203, 724, 2643, 9802, 36755, 138935, 528406, 2019419, 7748125, 29825844, 115132729, 445498768, 1727434607, 6710501025, 26110567532, 101744332967, 396983837719, 1550777652546, 6064476854065, 23739056348161]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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