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 | 4 |
| 3 | 9 |
| 4 | 224 |
| 5 | 1650 |
| 6 | 38664 |
| 7 | 540960 |
| 8 | 13930496 |
| 9 | 291769128 |
| 10 | 8598924000 |
| 11 | 237964577400 |
| 12 | 8082061452288 |
| 13 | 275311724996880 |
| 14 | 10714824398213376 |
| 15 | 430458433091505000 |
| 16 | 19007133744632954880 |
| 17 | 876046954673290438080 |
| 18 | 43416883192646088235008 |
| 19 | 2252711496770428822876800 |
| 20 | 124040138653975179571200000 |