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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.

A345105 a(n) = 1 + 3 * Sum_{k=0..n-1} binomial(n-1,k) * a(k) * a(n-k-1).

Table of values

n a(n)
0 1
1 4
2 25
3 247
4 3283
5 54661
6 1092427
7 25473037
8 678837319
9 20351864821
10 677954261635
11 24842157250117
12 993040102321927
13 43003754679356941
14 2005536858420616963
15 100211634039201328381
16 5341144936822423446247
17 302468060262966258380773
18 18136282125753572653056355

List of values

[1, 4, 25, 247, 3283, 54661, 1092427, 25473037, 678837319, 20351864821, 677954261635, 24842157250117, 993040102321927, 43003754679356941, 2005536858420616963, 100211634039201328381, 5341144936822423446247, 302468060262966258380773, 18136282125753572653056355]

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

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