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 | 12 |
| 4 | 24 |
| 5 | 40 |
| 6 | 2220 |
| 7 | 15204 |
| 8 | 70672 |
| 9 | 1723824 |
| 10 | 22710420 |
| 11 | 202577980 |
| 12 | 3841065624 |
| 13 | 71221859592 |
| 14 | 994632663388 |
| 15 | 19005155049300 |
| 16 | 421055077585440 |
| 17 | 8033764197776224 |
| 18 | 172109549363348772 |
| 19 | 4285658639255113836 |
| 20 | 101794836650015825320 |
| 21 | 2516190299149752959160 |