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 | 3 |
| 3 | 12 |
| 4 | 64 |
| 5 | 420 |
| 6 | 3246 |
| 7 | 28798 |
| 8 | 288072 |
| 9 | 3205044 |
| 10 | 39234340 |
| 11 | 523821936 |
| 12 | 7572221328 |
| 13 | 117792884872 |
| 14 | 1961516974704 |
| 15 | 34807390821960 |
| 16 | 655594811020096 |
| 17 | 13060711726818768 |
| 18 | 274358217793164912 |
| 19 | 6060159633360214144 |
| 20 | 140404595387426964480 |