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 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 32 |
| 6 | 108 |
| 7 | 336 |
| 8 | 1036 |
| 9 | 3120 |
| 10 | 9540 |
| 11 | 29244 |
| 12 | 89768 |
| 13 | 274788 |
| 14 | 840936 |
| 15 | 2573972 |
| 16 | 7881922 |
| 17 | 24135000 |
| 18 | 73897320 |
| 19 | 226249264 |
| 20 | 692714696 |
| 21 | 2120941424 |
| 22 | 6493883944 |
| 23 | 19882820480 |
| 24 | 60876609464 |
| 25 | 186390208744 |
| 26 | 570684661408 |
| 27 | 1747307671896 |
| 28 | 5349860697088 |