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 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 84 |
| 4 | 396 |
| 5 | 1872 |
| 6 | 8856 |
| 7 | 41904 |
| 8 | 198288 |
| 9 | 938304 |
| 10 | 4440096 |
| 11 | 21010752 |
| 12 | 99423936 |
| 13 | 470479104 |
| 14 | 2226331008 |
| 15 | 10535111424 |
| 16 | 49852682496 |
| 17 | 235905426432 |
| 18 | 1116316463616 |
| 19 | 5282466223104 |
| 20 | 24996898556928 |
| 21 | 118286594002944 |