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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.

A221954 a(n) = 3^(n-1) * n! * Catalan(n-1).

Table of values

n a(n)
1 1
2 6
3 108
4 3240
5 136080
6 7348320
7 484989120
8 37829151360
9 3404623622400
10 347271609484800
11 39588963481267200
12 4988209398639667200
13 688372897012274073600
14 103255934551841111040000
15 16727461397398259988480000
16 2910578283147297237995520000
17 541367560665397286267166720000
18 107190777011748662680899010560000
19 22510063172467219162988792217600000

List of values

[1, 6, 108, 3240, 136080, 7348320, 484989120, 37829151360, 3404623622400, 347271609484800, 39588963481267200, 4988209398639667200, 688372897012274073600, 103255934551841111040000, 16727461397398259988480000, 2910578283147297237995520000, 541367560665397286267166720000, 107190777011748662680899010560000, 22510063172467219162988792217600000]

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

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