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.

A000111 Euler or up/down numbers: e.g.f. sec(x) + tan(x). Also for n >= 2, half the number of alternating permutations on n letters (A001250).

Table of values

n a(n)
0 1
1 1
2 1
3 2
4 5
5 16
6 61
7 272
8 1385
9 7936
10 50521
11 353792
12 2702765
13 22368256
14 199360981
15 1903757312
16 19391512145
17 209865342976
18 2404879675441
19 29088885112832
20 370371188237525
21 4951498053124096
22 69348874393137901
23 1015423886506852352
24 15514534163557086905
25 246921480190207983616
26 4087072509293123892361

List of values

[1, 1, 1, 2, 5, 16, 61, 272, 1385, 7936, 50521, 353792, 2702765, 22368256, 199360981, 1903757312, 19391512145, 209865342976, 2404879675441, 29088885112832, 370371188237525, 4951498053124096, 69348874393137901, 1015423886506852352, 15514534163557086905, 246921480190207983616, 4087072509293123892361]

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

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