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 | 3 |
| 2 | 15 |
| 3 | 100 |
| 4 | 753 |
| 5 | 6006 |
| 6 | 49456 |
| 7 | 415422 |
| 8 | 3536802 |
| 9 | 30404161 |
| 10 | 263271639 |
| 11 | 2292524970 |
| 12 | 20052238465 |
| 13 | 176029542285 |
| 14 | 1549916592645 |
| 15 | 13681091072620 |
| 16 | 121020187476717 |
| 17 | 1072477163769417 |
| 18 | 9519299301332377 |
| 19 | 84609930915003882 |
| 20 | 752947626436806021 |
| 21 | 6707715814093174588 |