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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 6 |
| 7 | 24 |
| 8 | 118 |
| 9 | 714 |
| 10 | 5016 |
| 11 | 40200 |
| 12 | 362163 |
| 13 | 3623772 |
| 14 | 39876540 |
| 15 | 478639080 |
| 16 | 6223394516 |
| 17 | 87138394540 |
| 18 | 1307195547720 |
| 19 | 20916564680760 |
| 20 | 355600269756485 |
| 21 | 6401066270800350 |
| 22 | 121624180731849810 |
| 23 | 2432546364331038480 |
| 24 | 51084540451761077514 |
| 25 | 1123879093137556106358 |