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 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 5 |
| 5 | 17 |
| 6 | 51 |
| 7 | 148 |
| 8 | 429 |
| 9 | 1250 |
| 10 | 3655 |
| 11 | 10701 |
| 12 | 31336 |
| 13 | 91752 |
| 14 | 268623 |
| 15 | 786414 |
| 16 | 2302262 |
| 17 | 6739984 |
| 18 | 19731685 |
| 19 | 57765711 |
| 20 | 169112717 |
| 21 | 495088023 |
| 22 | 1449400960 |
| 23 | 4243211207 |
| 24 | 12422263776 |
| 25 | 36366946961 |
| 26 | 106466490879 |
| 27 | 311687250156 |