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 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 106 |
| 5 | 720 |
| 6 | 5085 |
| 7 | 37493 |
| 8 | 284331 |
| 9 | 2204973 |
| 10 | 17404720 |
| 11 | 139369905 |
| 12 | 1129411314 |
| 13 | 9244823986 |
| 14 | 76326154857 |
| 15 | 634847759955 |
| 16 | 5314684735045 |
| 17 | 44746683774474 |
| 18 | 378652035541761 |
| 19 | 3218705637379698 |
| 20 | 27471657413667780 |