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 | 0 |
| 1 | 2 |
| 2 | 20 |
| 3 | 126 |
| 4 | 648 |
| 5 | 2970 |
| 6 | 12636 |
| 7 | 51030 |
| 8 | 198288 |
| 9 | 747954 |
| 10 | 2755620 |
| 11 | 9959598 |
| 12 | 35429400 |
| 13 | 124357194 |
| 14 | 431530092 |
| 15 | 1482720390 |
| 16 | 5050815264 |
| 17 | 17075199330 |
| 18 | 57338232372 |
| 19 | 191385721566 |
| 20 | 635369601960 |
| 21 | 2099044209402 |
| 22 | 6903833113980 |