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 | 3 |
| 3 | 12 |
| 4 | 60 |
| 5 | 360 |
| 6 | 2418 |
| 7 | 19344 |
| 8 | 159120 |
| 9 | 1481040 |
| 10 | 15334088 |
| 11 | 184009056 |
| 12 | 2217441408 |
| 13 | 31044179712 |
| 14 | 442487616480 |
| 15 | 6686252969760 |
| 16 | 107004539285280 |
| 17 | 1926081707135040 |
| 18 | 34683832925921088 |
| 19 | 693676658518421760 |
| 20 | 13891399238731734720 |
| 21 | 292460416142501376000 |