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.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | -1 |
| 4 | 1 |
| 5 | -5 |
| 6 | 7 |
| 7 | -21 |
| 8 | 11 |
| 9 | -429 |
| 10 | 715 |
| 11 | -2431 |
| 12 | 4199 |
| 13 | -29393 |
| 14 | 52003 |
| 15 | -185725 |
| 16 | 334305 |
| 17 | -3231615 |
| 18 | 3535767 |
| 19 | -64822395 |
| 20 | 39803225 |
| 21 | -883631595 |
| 22 | 1641030105 |
| 23 | -407771117 |
| 24 | 11435320455 |
| 25 | -171529806825 |
| 26 | 107492012277 |
| 27 | -1215486600363 |
| 28 | 2295919134019 |