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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.

A133789 Let P(A) denote 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 x is not a subset of y and y is not a subset of x, 1) x and y are disjoint and for which either x is a subset of y or y is a subset of x, or 2) x and y intersect but for which x is not a subset of y and y is not a subset of x.

Table of values

n a(n)
0 0
1 1
2 4
3 16
4 70
5 316
6 1414
7 6196
8 26590
9 112156
10 466774
11 1923076
12 7863310
13 31972396
14 129459334
15 522571156
16 2104535230
17 8460991036
18 33972711094
19 136277478436
20 546270602350
21 2188566048076
22 8764718254054
23 35090241492916
24 140455083984670
25 562102715143516

List of values

[0, 1, 4, 16, 70, 316, 1414, 6196, 26590, 112156, 466774, 1923076, 7863310, 31972396, 129459334, 522571156, 2104535230, 8460991036, 33972711094, 136277478436, 546270602350, 2188566048076, 8764718254054, 35090241492916, 140455083984670, 562102715143516]

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

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