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 | 6 |
| 3 | 40 |
| 4 | 264 |
| 5 | 1744 |
| 6 | 11520 |
| 7 | 76096 |
| 8 | 502656 |
| 9 | 3320320 |
| 10 | 21932544 |
| 11 | 144876544 |
| 12 | 956989440 |
| 13 | 6321442816 |
| 14 | 41756614656 |
| 15 | 275825459200 |
| 16 | 1821979213824 |
| 17 | 12035177119744 |
| 18 | 79498979573760 |
| 19 | 525134585921536 |
| 20 | 3468803433824256 |