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 | 4 |
| 3 | 24 |
| 4 | 212 |
| 5 | 1080 |
| 6 | 18672 |
| 7 | 94584 |
| 8 | 2182752 |
| 9 | 21261708 |
| 10 | 408988080 |
| 11 | 3245265144 |
| 12 | 168549358368 |
| 13 | 1053716696760 |
| 14 | 42565371692592 |
| 15 | 921132763909200 |
| 16 | 26578273403903040 |
| 17 | 260741534058271800 |
| 18 | 20313207979498492344 |
| 19 | 185603174638656822264 |
| 20 | 16066126777465282744800 |
| 21 | 324499299994016295338064 |