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 | 20 |
| 3 | 145 |
| 4 | 1250 |
| 5 | 11746 |
| 6 | 116641 |
| 7 | 1204039 |
| 8 | 12790067 |
| 9 | 138895021 |
| 10 | 1535005454 |
| 11 | 17207743738 |
| 12 | 195197256289 |
| 13 | 2236419124408 |
| 14 | 25842382083071 |
| 15 | 300822398531482 |
| 16 | 3524358836945936 |
| 17 | 41524956284752018 |
| 18 | 491722951928324392 |
| 19 | 5848997420625891294 |
| 20 | 69854562522309219081 |