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 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 132 |
| 5 | 900 |
| 6 | 11160 |
| 7 | 100800 |
| 8 | 1809360 |
| 9 | 25053840 |
| 10 | 608428800 |
| 11 | 8610386400 |
| 12 | 469291838400 |
| 13 | 7110609105600 |
| 14 | 404607162960000 |
| 15 | 13958116204032000 |
| 16 | 821937470818464000 |
| 17 | 17420311428103584000 |
| 18 | 2860701872247483264000 |
| 19 | 60029296274562398784000 |