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 | 0 |
| 2 | 4 |
| 3 | 20 |
| 4 | 84 |
| 5 | 336 |
| 6 | 1320 |
| 7 | 5148 |
| 8 | 20020 |
| 9 | 77792 |
| 10 | 302328 |
| 11 | 1175720 |
| 12 | 4576264 |
| 13 | 17829600 |
| 14 | 69535440 |
| 15 | 271455660 |
| 16 | 1060730100 |
| 17 | 4148633280 |
| 18 | 16239715800 |
| 19 | 63621474840 |
| 20 | 249436575960 |
| 21 | 978650680800 |
| 22 | 3842267672880 |
| 23 | 15094623000600 |
| 24 | 59335590776904 |
| 25 | 233373427269696 |