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 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 8 |
| 5 | 20 |
| 6 | 96 |
| 7 | 656 |
| 8 | 5568 |
| 9 | 48912 |
| 10 | 494080 |
| 11 | 5383552 |
| 12 | 65097600 |
| 13 | 840566080 |
| 14 | 11833898496 |
| 15 | 176621049600 |
| 16 | 2838024476672 |
| 17 | 48060623405312 |
| 18 | 868000333234176 |
| 19 | 16441638519762944 |
| 20 | 329723762151352320 |
| 21 | 6907027877807330304 |