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 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | 6 |
| 7 | 42 |
| 8 | 336 |
| 9 | 3024 |
| 10 | 30366 |
| 11 | 335412 |
| 12 | 4041576 |
| 13 | 52756704 |
| 14 | 741620880 |
| 15 | 11169844686 |
| 16 | 179448036768 |
| 17 | 3063069801792 |
| 18 | 55360031126400 |
| 19 | 1056123043335360 |
| 20 | 21208345049147256 |
| 21 | 447183762148547424 |
| 22 | 9877939209960101280 |
| 23 | 228112734232663600320 |