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 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 16 |
| 5 | 66 |
| 6 | 280 |
| 7 | 1216 |
| 8 | 5384 |
| 9 | 24224 |
| 10 | 110464 |
| 11 | 509480 |
| 12 | 2372704 |
| 13 | 11142656 |
| 14 | 52709600 |
| 15 | 250933120 |
| 16 | 1201354240 |
| 17 | 5780413760 |
| 18 | 27937867520 |
| 19 | 135574988800 |
| 20 | 660314620160 |
| 21 | 3226731934720 |
| 22 | 15815752724480 |
| 23 | 77735943378560 |