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 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 120 |
| 5 | 720 |
| 6 | 4920 |
| 7 | 37320 |
| 8 | 309120 |
| 9 | 2763720 |
| 10 | 26440920 |
| 11 | 268864320 |
| 12 | 2889978120 |
| 13 | 32689371720 |
| 14 | 387638491920 |
| 15 | 4803456571320 |
| 16 | 62026296732120 |
| 17 | 832595493624720 |
| 18 | 11592967532632920 |
| 19 | 167119530011233320 |
| 20 | 2489936579950221120 |
| 21 | 38283169922493447720 |