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 | 60 |
| 6 | 1080 |
| 7 | 1680 |
| 8 | 80640 |
| 9 | 1058400 |
| 10 | 8316000 |
| 11 | 257463360 |
| 12 | 3692304000 |
| 13 | 66421555200 |
| 14 | 1801442522880 |
| 15 | 34333457558400 |
| 16 | 905811504998400 |
| 17 | 25171307671910400 |
| 18 | 646170363904665600 |
| 19 | 20523302430017587200 |
| 20 | 637272191855819520000 |
| 21 | 20620406757762459648000 |