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 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 24 |
| 7 | 144 |
| 8 | 312 |
| 9 | 1080 |
| 10 | 4632 |
| 11 | 24240 |
| 12 | 9264 |
| 13 | 57744 |
| 14 | 134016 |
| 15 | 517536 |
| 16 | 2338176 |
| 17 | 12725952 |
| 18 | 7014528 |
| 19 | 45192384 |
| 20 | 111428352 |
| 21 | 469862208 |
| 22 | 2213733888 |
| 23 | 12478256064 |
| 24 | 8854935552 |
| 25 | 58767959808 |
| 26 | 152955661824 |
| 27 | 693938824704 |