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 | 3 |
| 2 | 15 |
| 3 | 75 |
| 4 | 371 |
| 5 | 1833 |
| 6 | 9057 |
| 7 | 44753 |
| 8 | 221137 |
| 9 | 1092699 |
| 10 | 5399327 |
| 11 | 26679563 |
| 12 | 131831075 |
| 13 | 651413681 |
| 14 | 3218814561 |
| 15 | 15905050017 |
| 16 | 78591236385 |
| 17 | 388340962771 |
| 18 | 1918899743823 |
| 19 | 9481812581835 |
| 20 | 46852249642771 |