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 | 3 |
| 2 | 15 |
| 3 | 84 |
| 4 | 495 |
| 5 | 3003 |
| 6 | 18564 |
| 7 | 116280 |
| 8 | 735471 |
| 9 | 4686825 |
| 10 | 30045015 |
| 11 | 193536720 |
| 12 | 1251677700 |
| 13 | 8122425444 |
| 14 | 52860229080 |
| 15 | 344867425584 |
| 16 | 2254848913647 |
| 17 | 14771069086725 |
| 18 | 96926348578605 |
| 19 | 636983969321700 |
| 20 | 4191844505805495 |
| 21 | 27619435402363035 |