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 | 4 |
| 3 | 26 |
| 4 | 210 |
| 5 | 1897 |
| 6 | 18368 |
| 7 | 186636 |
| 8 | 1965414 |
| 9 | 21277685 |
| 10 | 235493544 |
| 11 | 2653779856 |
| 12 | 30357956720 |
| 13 | 351719984280 |
| 14 | 4119552129280 |
| 15 | 48708104589368 |
| 16 | 580682799531822 |
| 17 | 6973356315752445 |
| 18 | 84286657672243880 |
| 19 | 1024694111031383100 |
| 20 | 12522664914160322460 |
| 21 | 153762682439070435390 |