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 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 108 |
| 6 | 544 |
| 7 | 3264 |
| 8 | 23040 |
| 9 | 176832 |
| 10 | 1563392 |
| 11 | 15536160 |
| 12 | 171172224 |
| 13 | 2066033472 |
| 14 | 27146652480 |
| 15 | 385447394880 |
| 16 | 5878028516736 |
| 17 | 95776238793504 |
| 18 | 1660164417866304 |
| 19 | 30496085473606944 |
| 20 | 591661117634375040 |
| 21 | 12087628978334638752 |