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 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 54 |
| 6 | 429 |
| 7 | 4252 |
| 8 | 50605 |
| 9 | 703388 |
| 10 | 11184597 |
| 11 | 200247446 |
| 12 | 3986363597 |
| 13 | 87343744490 |
| 14 | 2088739037209 |
| 15 | 54134344486296 |
| 16 | 1511446306795417 |
| 17 | 45227224242345336 |
| 18 | 1443916049346447913 |
| 19 | 48989635949583331658 |
| 20 | 1760229264304229244753 |
| 21 | 66770472164443344587550 |