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 | 1 |
| 3 | 2 |
| 4 | 10 |
| 5 | 50 |
| 6 | 230 |
| 7 | 1260 |
| 8 | 9240 |
| 9 | 76440 |
| 10 | 651000 |
| 11 | 6006000 |
| 12 | 62739600 |
| 13 | 719518800 |
| 14 | 8736327600 |
| 15 | 112588476000 |
| 16 | 1558917360000 |
| 17 | 23070967920000 |
| 18 | 360507459312000 |
| 19 | 5925688056288000 |
| 20 | 102619150714080000 |
| 21 | 1869557514945120000 |
| 22 | 35676360727207200000 |