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 | 12 |
| 5 | 40 |
| 6 | 5220 |
| 7 | 41328 |
| 8 | 339360 |
| 9 | 28477440 |
| 10 | 489877920 |
| 11 | 7325176320 |
| 12 | 501467630400 |
| 13 | 14323336634880 |
| 14 | 333439476289920 |
| 15 | 21001701037363200 |
| 16 | 849627551212876800 |
| 17 | 27872303353627299840 |
| 18 | 1742879646852427791360 |
| 19 | 90170933394707691724800 |