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 | 4 |
| 4 | 3 |
| 5 | 192 |
| 6 | 20 |
| 7 | 11520 |
| 8 | 315 |
| 9 | 573440 |
| 10 | 36288 |
| 11 | 928972800 |
| 12 | 1663200 |
| 13 | 54499737600 |
| 14 | 74131200 |
| 15 | 1322526965760 |
| 16 | 6810804000 |
| 17 | 228532659683328000 |
| 18 | 37638881280 |
| 19 | 16783438527143608320 |
| 20 | 121645100408832 |
| 21 | 30370031620545576960000 |