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 | 1 |
| 3 | 3 |
| 4 | 16 |
| 5 | 124 |
| 6 | 1256 |
| 7 | 15576 |
| 8 | 226248 |
| 9 | 3729216 |
| 10 | 68179968 |
| 11 | 1361836800 |
| 12 | 29501349120 |
| 13 | 693638208000 |
| 14 | 17815908096000 |
| 15 | 502048890201600 |
| 16 | 15388268595840000 |
| 17 | 500579319427891200 |
| 18 | 16817771937344716800 |
| 19 | 581609175119297740800 |