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 | 3 |
| 4 | 6 |
| 5 | 20 |
| 6 | 180 |
| 7 | 1134 |
| 8 | 7980 |
| 9 | 71280 |
| 10 | 685440 |
| 11 | 7165620 |
| 12 | 82720440 |
| 13 | 1036404720 |
| 14 | 13990472496 |
| 15 | 202812132600 |
| 16 | 3141926096400 |
| 17 | 51795939162240 |
| 18 | 905465629762560 |
| 19 | 16731527824735920 |
| 20 | 325859956191352800 |
| 21 | 6671593966263992640 |
| 22 | 143254214818174152000 |