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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.

A260504 Number of chains in the poset of all odd-sized subsets of {1,2,...,n} ordered by inclusion.

Table of values

n a(n)
0 0
1 1
2 2
3 7
4 20
5 91
6 362
7 2227
8 11720
9 92491
10 608222
11 5866147
12 46290620
13 527635291
14 4857587282
15 63886537267
16 672183848720
17 10019232896491
18 118594819341542
19 1975680877259587
20 25983971598078020
21 478434297205284091
22 6921555837554655002
23 139581878985127217107

List of values

[0, 1, 2, 7, 20, 91, 362, 2227, 11720, 92491, 608222, 5866147, 46290620, 527635291, 4857587282, 63886537267, 672183848720, 10019232896491, 118594819341542, 1975680877259587, 25983971598078020, 478434297205284091, 6921555837554655002, 139581878985127217107]

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

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