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 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 105 |
| 5 | 945 |
| 6 | 10395 |
| 7 | 135135 |
| 8 | 2027025 |
| 9 | 34459425 |
| 10 | 654729075 |
| 11 | 4583103525 |
| 12 | 34788783519 |
| 13 | 286302699633 |
| 14 | 2541730502259 |
| 15 | 24202811629589 |
| 16 | 245427373661087 |
| 17 | 2620070906538825 |
| 18 | 28854865779691475 |
| 19 | 317259847008270825 |
| 20 | 3336850194636528659 |
| 21 | 32503486859882091945 |