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 | 2520 |
| 8 | 241920 |
| 9 | 3674160 |
| 10 | 12700800 |
| 11 | 599749920 |
| 12 | 7903526400 |
| 13 | 77863705920 |
| 14 | 2660390853120 |
| 15 | 37269497865600 |
| 16 | 683129089843200 |
| 17 | 19948163057222400 |
| 18 | 339567800885913600 |
| 19 | 8690022866119795200 |
| 20 | 241333983478748160000 |
| 21 | 5217670959100125926400 |