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 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 17 |
| 4 | 69 |
| 5 | 204 |
| 6 | -330 |
| 7 | -12510 |
| 8 | -110250 |
| 9 | -42840 |
| 10 | 16760520 |
| 11 | 332942400 |
| 12 | 3258208800 |
| 13 | -13239903600 |
| 14 | -1299112214400 |
| 15 | -28283225770800 |
| 16 | -232265443410000 |
| 17 | 6756753459456000 |
| 18 | 338710300424496000 |
| 19 | 7139034325607184000 |
| 20 | 19827438602379408000 |
| 21 | -4654590583125843360000 |