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 | 2 |
| 4 | 6 |
| 5 | 44 |
| 6 | 210 |
| 7 | 1644 |
| 8 | 11088 |
| 9 | 119664 |
| 10 | 1034640 |
| 11 | 12372480 |
| 12 | 139629600 |
| 13 | 1877722560 |
| 14 | 25389131040 |
| 15 | 395162832960 |
| 16 | 6041860070400 |
| 17 | 105872058754560 |
| 18 | 1864694944465920 |
| 19 | 35822359116149760 |
| 20 | 705399920144640000 |
| 21 | 15048474234019430400 |
| 22 | 324762706938629836800 |
| 23 | 7566557300438795366400 |