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 | 6 |
| 3 | 18 |
| 4 | 108 |
| 5 | 324 |
| 6 | 1458 |
| 7 | 4374 |
| 8 | 17496 |
| 9 | 52488 |
| 10 | 196830 |
| 11 | 590490 |
| 12 | 2125764 |
| 13 | 6377292 |
| 14 | 22320522 |
| 15 | 66961566 |
| 16 | 229582512 |
| 17 | 688747536 |
| 18 | 2324522934 |
| 19 | 6973568802 |
| 20 | 23245229340 |
| 21 | 69735688020 |
| 22 | 230127770466 |
| 23 | 690383311398 |
| 24 | 2259436291848 |
| 25 | 6778308875544 |
| 26 | 22029503845518 |
| 27 | 66088511536554 |