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 | 3 |
| 3 | 15 |
| 4 | 63 |
| 5 | 213 |
| 6 | 687 |
| 7 | 2127 |
| 8 | 6483 |
| 9 | 19575 |
| 10 | 58905 |
| 11 | 176943 |
| 12 | 531177 |
| 13 | 1593981 |
| 14 | 4782513 |
| 15 | 14348289 |
| 16 | 43045923 |
| 17 | 129139119 |
| 18 | 387419097 |
| 19 | 1162259637 |
| 20 | 3486782013 |
| 21 | 10460350023 |
| 22 | 31381055463 |
| 23 | 94143173409 |