cp's OEIS Frontend

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.

A134988 Number of formal expressions obtained by applying iterated binary brackets to n indexed symbols x_1, ..., x_n such that: 1) each symbol appears exactly once; 2) the smallest index inside a bracket appears on the left hand side and the largest index appears on the right hand side; 3) the outer bracket is the only bracket whose set of indices is a sequence of consecutive integers.

Table of values

n a(n)
2 1
3 0
4 1
5 4
6 22
7 144
8 1089
9 9308
10 88562
11 927584
12 10603178
13 131368648
14 1753970380
15 25112732512
16 383925637137
17 6243618722124
18 107644162715098
19 1961478594977856
20 37671587406585006
21 760654555198989240
22 16110333600696417780
23 357148428086308848480
24 8271374327887650503130

List of values

[1, 0, 1, 4, 22, 144, 1089, 9308, 88562, 927584, 10603178, 131368648, 1753970380, 25112732512, 383925637137, 6243618722124, 107644162715098, 1961478594977856, 37671587406585006, 760654555198989240, 16110333600696417780, 357148428086308848480, 8271374327887650503130]

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

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