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 | 8 |
| 4 | 42 |
| 5 | 258 |
| 6 | 1824 |
| 7 | 14664 |
| 8 | 132360 |
| 9 | 1326120 |
| 10 | 14606640 |
| 11 | 175448160 |
| 12 | 2282469840 |
| 13 | 31972303440 |
| 14 | 479793807360 |
| 15 | 7679384173440 |
| 16 | 130586660507520 |
| 17 | 2351111258805120 |
| 18 | 44679858911251200 |
| 19 | 893744703503769600 |
| 20 | 18771276190401504000 |
| 21 | 413017883356110278400 |