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 | 0 |
| 1 | 1 |
| 2 | 12 |
| 3 | 110 |
| 4 | 912 |
| 5 | 7204 |
| 6 | 55440 |
| 7 | 420344 |
| 8 | 3159168 |
| 9 | 23618320 |
| 10 | 176008128 |
| 11 | 1309074656 |
| 12 | 9724619520 |
| 13 | 72186895936 |
| 14 | 535605687552 |
| 15 | 3972913788800 |
| 16 | 29464372088832 |
| 17 | 218493396246784 |
| 18 | 1620132103941120 |
| 19 | 12012809774902784 |
| 20 | 89069225764835328 |