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 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 72 |
| 5 | 840 |
| 6 | 12780 |
| 7 | 238770 |
| 8 | 5281920 |
| 9 | 134946000 |
| 10 | 3909578400 |
| 11 | 126638542800 |
| 12 | 4535037460800 |
| 13 | 177904622095200 |
| 14 | 7586967310322400 |
| 15 | 349479111223242000 |
| 16 | 17292052928037888000 |
| 17 | 914673660594613920000 |
| 18 | 51506610632458293312000 |
| 19 | 3076341001739003430432000 |