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 | 2 |
| 3 | 3 |
| 4 | 32 |
| 5 | 150 |
| 6 | 1524 |
| 7 | 12600 |
| 8 | 147328 |
| 9 | 1705536 |
| 10 | 23681520 |
| 11 | 345605040 |
| 12 | 5654922624 |
| 13 | 98624766240 |
| 14 | 1870594556544 |
| 15 | 37794037488480 |
| 16 | 817362198512640 |
| 17 | 18742996919324160 |
| 18 | 455648694329309184 |
| 19 | 11683777530785978880 |
| 20 | 315505598702787118080 |
| 21 | 8943481464393674096640 |