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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 36 |
| 5 | 264 |
| 6 | 2335 |
| 7 | 23609 |
| 8 | 272880 |
| 9 | 3543360 |
| 10 | 51123511 |
| 11 | 811313945 |
| 12 | 14045781456 |
| 13 | 263429150544 |
| 14 | 5320671461575 |
| 15 | 115141595216009 |
| 16 | 2657827340717760 |
| 17 | 65185383511024320 |
| 18 | 1692767331624879031 |
| 19 | 46400793659613081785 |
| 20 | 1338843898122140977776 |
| 21 | 40562412499251225624624 |