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 | 4 |
| 3 | 24 |
| 4 | 198 |
| 5 | 2070 |
| 6 | 26160 |
| 7 | 387240 |
| 8 | 6565020 |
| 9 | 125341020 |
| 10 | 2659925520 |
| 11 | 62089917120 |
| 12 | 1580632348680 |
| 13 | 43571319671880 |
| 14 | 1292731109429760 |
| 15 | 41068078953501600 |
| 16 | 1390717740470058000 |
| 17 | 50003952605673066000 |
| 18 | 1902359109096675028800 |
| 19 | 76341746199227491382400 |