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) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 24 |
| 5 | 129 |
| 6 | 840 |
| 7 | 5265 |
| 8 | 40320 |
| 9 | 434385 |
| 10 | 3900960 |
| 11 | 40809825 |
| 12 | 558835200 |
| 13 | 6335076825 |
| 14 | 91070179200 |
| 15 | 1641957141825 |
| 16 | 20922789888000 |
| 17 | 359796258446625 |
| 18 | 7663952552256000 |
| 19 | 122832552380162625 |
| 20 | 2615369658789888000 |
| 21 | 62315614994643635625 |