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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.

A187761 Number of maps f: [n] -> [n] with f(x)<=x and f(f(x)) = f(f(f(x))).

Table of values

n a(n)
0 1
1 1
2 2
3 6
4 23
5 106
6 568
7 3459
8 23544
9 176850
10 1451253
11 12904312
12 123489888
13 1264591561
14 13790277294
15 159466823794
16 1948259002647
17 25066729706582
18 338670605492700
19 4792623436607059
20 70873649458154500
21 1092969062435462254
22 17543703470388927229
23 292600906102204630092

List of values

[1, 1, 2, 6, 23, 106, 568, 3459, 23544, 176850, 1451253, 12904312, 123489888, 1264591561, 13790277294, 159466823794, 1948259002647, 25066729706582, 338670605492700, 4792623436607059, 70873649458154500, 1092969062435462254, 17543703470388927229, 292600906102204630092]

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

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