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 | 2 |
| 3 | 6 |
| 4 | 12 |
| 5 | 30 |
| 6 | 90 |
| 7 | 420 |
| 8 | 2240 |
| 9 | 13440 |
| 10 | 84000 |
| 11 | 577500 |
| 12 | 4331250 |
| 13 | 36036000 |
| 14 | 322882560 |
| 15 | 3099672576 |
| 16 | 31513337856 |
| 17 | 340409701632 |
| 18 | 3893435962416 |
| 19 | 47122428697344 |
| 20 | 600341948743680 |
| 21 | 8030803773358080 |
| 22 | 112453396587417600 |
| 23 | 1646232972560748000 |
| 24 | 25147419121286426250 |