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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.

A051924 a(n) = binomial(2*n,n) - binomial(2*n-2,n-1); or (3n-2)*C(n-1), where C = Catalan numbers (A000108).

Table of values

n a(n)
1 1
2 4
3 14
4 50
5 182
6 672
7 2508
8 9438
9 35750
10 136136
11 520676
12 1998724
13 7696444
14 29716000
15 115000920
16 445962870
17 1732525830
18 6741529080
19 26270128500
20 102501265020
21 400411345620
22 1565841089280
23 6129331763880
24 24014172955500
25 94163002754652
26 369507926510352

List of values

[1, 4, 14, 50, 182, 672, 2508, 9438, 35750, 136136, 520676, 1998724, 7696444, 29716000, 115000920, 445962870, 1732525830, 6741529080, 26270128500, 102501265020, 400411345620, 1565841089280, 6129331763880, 24014172955500, 94163002754652, 369507926510352]

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

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