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 | -2 |
| 3 | -3 |
| 4 | 16 |
| 5 | -10 |
| 6 | -114 |
| 7 | 462 |
| 8 | -496 |
| 9 | -2952 |
| 10 | 16920 |
| 11 | -31680 |
| 12 | -130008 |
| 13 | 1707576 |
| 14 | -14259504 |
| 15 | 138375720 |
| 16 | -1652311680 |
| 17 | 22238105280 |
| 18 | -321916019904 |
| 19 | 4959460972224 |
| 20 | -81123831838080 |
| 21 | 1405677742882560 |
| 22 | -25732182778727040 |
| 23 | 496324987642915200 |
| 24 | -10061966722201900416 |