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 | 136 |
| 5 | 720 |
| 6 | 3624 |
| 7 | 17584 |
| 8 | 83024 |
| 9 | 383904 |
| 10 | 1746280 |
| 11 | 7839216 |
| 12 | 34812144 |
| 13 | 153204064 |
| 14 | 669108496 |
| 15 | 2903267040 |
| 16 | 12526343584 |
| 17 | 53779871552 |
| 18 | 229895033832 |
| 19 | 978965187184 |
| 20 | 4154438114480 |
| 21 | 17575883030496 |
| 22 | 74150192517808 |