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 | 9 |
| 2 | 40 |
| 3 | 200 |
| 4 | 952 |
| 5 | 4624 |
| 6 | 22272 |
| 7 | 107648 |
| 8 | 519552 |
| 9 | 2509056 |
| 10 | 12113920 |
| 11 | 58492928 |
| 12 | 282425344 |
| 13 | 1363677184 |
| 14 | 6584401920 |
| 15 | 31792332800 |
| 16 | 153506906112 |
| 17 | 741197021184 |
| 18 | 3578815578112 |
| 19 | 17280050659328 |
| 20 | 83435464425472 |