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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.

A187980 Number of nondecreasing arrangements of n numbers x(i) in -(n-1)..(n-1) with the sum of sign(x(i))*2^|x(i)| zero.

Table of values

n a(n)
1 0
2 1
3 3
4 9
5 36
6 117
7 411
8 1452
9 5040
10 17829
11 62870
12 222458
13 789895
14 2808018
15 10006020
16 35713288
17 127657287
18 456975112
19 1637845137
20 5876993799
21 21110257429
22 75900966585
23 273140226328
24 983733709424
25 3545658087397
26 12788512426396
27 46155740640489
28 166684398100813
29 602296651467057
30 2177492178467267
31 7876245417001355

List of values

[0, 1, 3, 9, 36, 117, 411, 1452, 5040, 17829, 62870, 222458, 789895, 2808018, 10006020, 35713288, 127657287, 456975112, 1637845137, 5876993799, 21110257429, 75900966585, 273140226328, 983733709424, 3545658087397, 12788512426396, 46155740640489, 166684398100813, 602296651467057, 2177492178467267, 7876245417001355]

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

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