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 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 81 |
| 5 | 405 |
| 6 | 1944 |
| 7 | 9477 |
| 8 | 45927 |
| 9 | 223074 |
| 10 | 1082565 |
| 11 | 5255361 |
| 12 | 25509168 |
| 13 | 123825753 |
| 14 | 601059771 |
| 15 | 2917611090 |
| 16 | 14162371209 |
| 17 | 68745613437 |
| 18 | 333698181192 |
| 19 | 1619805064509 |
| 20 | 7862698824255 |
| 21 | 38166342053346 |
| 22 | 185263315578333 |