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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 75 |
| 6 | 495 |
| 7 | 3465 |
| 8 | 29295 |
| 9 | 263655 |
| 10 | 2735775 |
| 11 | 30093525 |
| 12 | 370945575 |
| 13 | 4822292475 |
| 14 | 68916822975 |
| 15 | 1033752344625 |
| 16 | 16813959537375 |
| 17 | 285837312135375 |
| 18 | 5214921734397375 |
| 19 | 99083512953550125 |
| 20 | 2004231846526284375 |
| 21 | 42088868777051971875 |
| 22 | 934957186489800849375 |