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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.

A134045 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 = y.

Table of values

n a(n)
0 1
1 3
2 7
3 18
4 61
5 258
6 1177
7 5358
8 23821
9 103338
10 439297
11 1838598
12 7605781
13 31191618
14 127100617
15 515462238
16 2083142941
17 8396683098
18 33779525137
19 135697396278
20 544529307301
21 2183340065778
22 8749036112857
23 35043186680718
24 140313902770861
25 561679137947658
26 2247987249823777
27 8995761328275558

List of values

[1, 3, 7, 18, 61, 258, 1177, 5358, 23821, 103338, 439297, 1838598, 7605781, 31191618, 127100617, 515462238, 2083142941, 8396683098, 33779525137, 135697396278, 544529307301, 2183340065778, 8749036112857, 35043186680718, 140313902770861, 561679137947658, 2247987249823777, 8995761328275558]

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

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