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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.

A134168 Let P(A) be the power set of an n-element set A. Then a(n) = the number of pairs of elements {x,y} of P(A) for which either 0) x and y are disjoint and for which either x is a subset of y or y is a subset of x, or 1) x and y are intersecting but for which x is not a subset of y and y is not a subset of x, or 2) x and y are intersecting and for which either x is a proper subset of y or y is a proper subset of x, or 3) x = y.

Table of values

n a(n)
0 1
1 3
2 9
3 30
4 111
5 438
6 1779
7 7290
8 29871
9 121998
10 496299
11 2011650
12 8129031
13 32769558
14 131850819
15 529745610
16 2126058591
17 8525561118
18 34166421339
19 136858609170
20 548013994551
21 2193796224678
22 8780408783859
23 35137313082330
24 140596298752911
25 562526359448238
26 2250528981434379
27 9003386657325090

List of values

[1, 3, 9, 30, 111, 438, 1779, 7290, 29871, 121998, 496299, 2011650, 8129031, 32769558, 131850819, 529745610, 2126058591, 8525561118, 34166421339, 136858609170, 548013994551, 2193796224678, 8780408783859, 35137313082330, 140596298752911, 562526359448238, 2250528981434379, 9003386657325090]

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