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) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -5 |
| 5 | 7 |
| 6 | -21 |
| 7 | 33 |
| 8 | -429 |
| 9 | 715 |
| 10 | -2431 |
| 11 | 4199 |
| 12 | -29393 |
| 13 | 52003 |
| 14 | -185725 |
| 15 | 334305 |
| 16 | -9694845 |
| 17 | 17678835 |
| 18 | -64822395 |
| 19 | 119409675 |
| 20 | -883631595 |
| 21 | 1641030105 |
| 22 | -6116566755 |
| 23 | 11435320455 |
| 24 | -171529806825 |
| 25 | 322476036831 |
| 26 | -1215486600363 |
| 27 | 2295919134019 |