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) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 20 |
| 4 | 182 |
| 5 | 1640 |
| 6 | 14762 |
| 7 | 132860 |
| 8 | 1195742 |
| 9 | 10761680 |
| 10 | 96855122 |
| 11 | 871696100 |
| 12 | 7845264902 |
| 13 | 70607384120 |
| 14 | 635466457082 |
| 15 | 5719198113740 |
| 16 | 51472783023662 |
| 17 | 463255047212960 |
| 18 | 4169295424916642 |
| 19 | 37523658824249780 |
| 20 | 337712929418248022 |