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 | 6 |
| 4 | 72 |
| 5 | 360 |
| 6 | 1080 |
| 7 | 15120 |
| 8 | 302400 |
| 9 | 3689280 |
| 10 | 32659200 |
| 11 | 359251200 |
| 12 | 6965481600 |
| 13 | 133880947200 |
| 14 | 2070484416000 |
| 15 | 30305353478400 |
| 16 | 559684629504000 |
| 17 | 12582442768896000 |
| 18 | 271843009108070400 |
| 19 | 5401042458152140800 |
| 20 | 111578968350001152000 |
| 21 | 2657164887872022528000 |