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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | -24 |
| 5 | -120 |
| 6 | -360 |
| 7 | -840 |
| 8 | 18480 |
| 9 | 359856 |
| 10 | 3623760 |
| 11 | 26603280 |
| 12 | 79821720 |
| 13 | -2283258120 |
| 14 | -61509151704 |
| 15 | -964150419960 |
| 16 | -10830864888480 |
| 17 | -60512343148320 |
| 18 | 1054627338811680 |
| 19 | 45270062235647136 |
| 20 | 995044394226238920 |
| 21 | 15575041436469437160 |