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 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 56 |
| 7 | 162 |
| 8 | 462 |
| 9 | 1306 |
| 10 | 3648 |
| 11 | 10116 |
| 12 | 27892 |
| 13 | 76524 |
| 14 | 209112 |
| 15 | 569506 |
| 16 | 1546542 |
| 17 | 4189314 |
| 18 | 11323480 |
| 19 | 30548190 |
| 20 | 82272330 |
| 21 | 221240070 |
| 22 | 594131160 |
| 23 | 1593553452 |
| 24 | 4269391596 |
| 25 | 11426761548 |
| 26 | 30554523096 |
| 27 | 81631135502 |
| 28 | 217918012002 |