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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 3 |
| 5 | 30 |
| 6 | 105 |
| 7 | 315 |
| 8 | 2625 |
| 9 | 11340 |
| 10 | 57645 |
| 11 | 467775 |
| 12 | 2505195 |
| 13 | 17027010 |
| 14 | 142026885 |
| 15 | 922296375 |
| 16 | 7493911425 |
| 17 | 65886420600 |
| 18 | 503693415225 |
| 19 | 4625660914875 |
| 20 | 43369908657075 |
| 21 | 379618464975750 |
| 22 | 3824934458169825 |
| 23 | 38406952928819475 |
| 24 | 376103907454500225 |