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 | 84 |
| 4 | 494 |
| 5 | 2988 |
| 6 | 18411 |
| 7 | 114950 |
| 8 | 724845 |
| 9 | 4606095 |
| 10 | 29451240 |
| 11 | 189264672 |
| 12 | 1221417360 |
| 13 | 7910510312 |
| 14 | 51388786107 |
| 15 | 334716829674 |
| 16 | 2185180379179 |
| 17 | 14294808917025 |
| 18 | 93680975707935 |
| 19 | 614925987859260 |
| 20 | 4042236129950970 |