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 | 8 |
| 5 | 36 |
| 6 | 180 |
| 7 | 1008 |
| 8 | 6336 |
| 9 | 46080 |
| 10 | 374400 |
| 11 | 3369600 |
| 12 | 32659200 |
| 13 | 344736000 |
| 14 | 3886444800 |
| 15 | 47348582400 |
| 16 | 611264102400 |
| 17 | 8442272563200 |
| 18 | 122595843686400 |
| 19 | 1890952003584000 |
| 20 | 30510694932480000 |
| 21 | 520011800985600000 |
| 22 | 9231875243458560000 |
| 23 | 172292221923655680000 |