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 | 4 |
| 4 | 13 |
| 5 | 56 |
| 6 | 301 |
| 7 | 1688 |
| 8 | 11705 |
| 9 | 84160 |
| 10 | 698521 |
| 11 | 6141312 |
| 12 | 59340997 |
| 13 | 613282944 |
| 14 | 6782462597 |
| 15 | 80158806016 |
| 16 | 1000434618609 |
| 17 | 13267800137728 |
| 18 | 184576848771889 |
| 19 | 2710082835353600 |
| 20 | 41577074746699261 |
| 21 | 669033814167273472 |