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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 9 |
| 4 | 108 |
| 5 | 3420 |
| 6 | 114480 |
| 7 | 7786800 |
| 8 | 497266560 |
| 9 | 42616445760 |
| 10 | 4320959126400 |
| 11 | 534444478444800 |
| 12 | 77699101730342400 |
| 13 | 13282131639801024000 |