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 | 0 |
| 3 | 6 |
| 4 | 0 |
| 5 | 30 |
| 6 | 540 |
| 7 | 420 |
| 8 | 15120 |
| 9 | 192780 |
| 10 | 623700 |
| 11 | 15467760 |
| 12 | 187110000 |
| 13 | 1394593200 |
| 14 | 30353483160 |
| 15 | 401350950000 |
| 16 | 4974611241600 |
| 17 | 105201040744800 |
| 18 | 1624218256861200 |
| 19 | 27525899782180800 |
| 20 | 599214125325816000 |
| 21 | 10967831645346576000 |
| 22 | 227431647445400798400 |