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 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 8 |
| 5 | 60 |
| 6 | 440 |
| 7 | 3290 |
| 8 | 25424 |
| 9 | 204120 |
| 10 | 1705680 |
| 11 | 14836470 |
| 12 | 134240040 |
| 13 | 1262060228 |
| 14 | 12313382536 |
| 15 | 124509169330 |
| 16 | 1303109358880 |
| 17 | 14098102762160 |
| 18 | 157473907149600 |
| 19 | 1813923418494126 |
| 20 | 21523529286435000 |
| 21 | 262809607270736540 |