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 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 20 |
| 6 | 90 |
| 7 | 630 |
| 8 | 3360 |
| 9 | 30240 |
| 10 | 226800 |
| 11 | 2494800 |
| 12 | 23950080 |
| 13 | 311351040 |
| 14 | 3632428800 |
| 15 | 54486432000 |
| 16 | 747242496000 |
| 17 | 12703122432000 |
| 18 | 200074178304000 |
| 19 | 3801409387776000 |
| 20 | 67580611338240000 |
| 21 | 1419192838103040000 |
| 22 | 28100018194440192000 |
| 23 | 646300418472124416000 |