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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.

A110104 a(n) is the number of coverings of 1..n by cyclic words of length 3n, such that each value from 1 to n appears precisely twice. That is, the union of all the letters in all of the words of a given covering is the multiset {1,1,2,2,...,n,n}. No repeats of words are allowed in a given covering.

Table of values

n a(n)
0 1
1 4
2 3760
3 23504320
4 567399078400
5 37518268781593600
6 5543744611870143078400
7 1599334510537656091623424000
8 818296434784062385011283591168000

List of values

[1, 4, 3760, 23504320, 567399078400, 37518268781593600, 5543744611870143078400, 1599334510537656091623424000, 818296434784062385011283591168000]

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

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