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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.

A117515 Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n).

Table of values

n a(n)
1 1
2 2
3 6
4 72
5 1240
6 33360

List of values

[1, 2, 6, 72, 1240, 33360]

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

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