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 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 9 |
| 5 | 54 |
| 6 | 0 |
| 7 | 0 |
| 8 | 52650 |
| 9 | 1890540 |
| 10 | 0 |
| 11 | 0 |
| 12 | 264480947280 |
| 13 | 57127543673760 |
| 14 | 0 |
| 15 | 0 |
| 16 | 1295355012667626301200 |
| 17 | 1678780080964997690732640 |
| 18 | 0 |
| 19 | 0 |
| 20 | 6577809875294796334824189267538944 |