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 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 125 |
| 6 | 750 |
| 7 | 5250 |
| 8 | 42001 |
| 9 | 378009 |
| 10 | 3780090 |
| 11 | 41580990 |
| 12 | 498971881 |
| 13 | 6486634453 |
| 14 | 90812882342 |
| 15 | 1362193235130 |
| 16 | 21795091762081 |
| 17 | 370516559955377 |
| 18 | 6669298079196786 |
| 19 | 126716663504738934 |
| 20 | 2534333270094778681 |
| 21 | 53220998671990352301 |
| 22 | 1170861970783787750622 |