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 | 18 |
| 4 | 0 |
| 5 | 180 |
| 6 | 4320 |
| 7 | 5040 |
| 8 | 241920 |
| 9 | 3900960 |
| 10 | 19958400 |
| 11 | 622702080 |
| 12 | 9580032000 |
| 13 | 112086374400 |
| 14 | 3013462932480 |
| 15 | 52540488000000 |
| 16 | 977094287769600 |
| 17 | 25683596370432000 |
| 18 | 540291743902310400 |
| 19 | 13061642656398336000 |
| 20 | 360218657273739264000 |
| 21 | 9111103133582241792000 |