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 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 3 |
| 5 | 39 |
| 6 | 357 |
| 7 | 2952 |
| 8 | 23622 |
| 9 | 186984 |
| 10 | 1474773 |
| 11 | 11617815 |
| 12 | 91485075 |
| 13 | 720308160 |
| 14 | 5671099008 |
| 15 | 44648794944 |
| 16 | 351520074867 |
| 17 | 2767513935927 |
| 18 | 21788596994037 |
| 19 | 171541276628904 |
| 20 | 1350541654293318 |
| 21 | 10632792057873480 |
| 22 | 83711795070905925 |
| 23 | 659061569195852295 |