cp's OEIS Frontend

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.

A280202 Number of topologies on an n-set X such that for all x in X there is a y in X such that x and y are topologically indistinguishable.

Table of values

n a(n)
0 1
1 0
2 1
3 1
4 10
5 31
6 361
7 2164
8 32663
9 313121
10 6199024
11 86219497
12 2225685925
13 42396094690
14 1414152064833
15 35520966967269
16 1517860883350266
17 48936884016265947
18 2659543345912283917
19 107827798819822505332
20 7409614386025588874195
21 371626299919138199117981

List of values

[1, 0, 1, 1, 10, 31, 361, 2164, 32663, 313121, 6199024, 86219497, 2225685925, 42396094690, 1414152064833, 35520966967269, 1517860883350266, 48936884016265947, 2659543345912283917, 107827798819822505332, 7409614386025588874195, 371626299919138199117981]

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

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