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 | 20 |
| 5 | 800 |
| 6 | 14260 |
| 7 | 189280 |
| 8 | 2181060 |
| 9 | 23241120 |
| 10 | 235737620 |
| 11 | 2308206560 |
| 12 | 21979728100 |
| 13 | 204477713440 |
| 14 | 1864504348980 |
| 15 | 16707856095840 |
| 16 | 147469451067140 |
| 17 | 1284607771225760 |
| 18 | 11063319237792340 |
| 19 | 94343562846289120 |
| 20 | 797685042851814180 |
| 21 | 6694943490279586080 |