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 | 4 |
| 2 | 8 |
| 3 | 20 |
| 4 | 560 |
| 5 | 560 |
| 6 | 440 |
| 7 | 7280 |
| 8 | 160160 |
| 9 | 2722720 |
| 10 | 51731680 |
| 11 | 51731680 |
| 12 | 45762640 |
| 13 | 1487285800 |
| 14 | 5949143200 |
| 15 | 86262576400 |
| 16 | 10696559473600 |
| 17 | 368846878400 |
| 18 | 562976814400 |
| 19 | 395772700523200 |
| 20 | 395772700523200 |
| 21 | 16226680721451200 |