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 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 8 |
| 6 | 252 |
| 7 | 4956 |
| 8 | 77992 |
| 9 | 1074564 |
| 10 | 13545216 |
| 11 | 160174960 |
| 12 | 1805010948 |
| 13 | 19588944336 |
| 14 | 206254571236 |
| 15 | 2118399516180 |
| 16 | 21310566266640 |
| 17 | 210636265153004 |
| 18 | 2050696768165560 |
| 19 | 19704531058696008 |
| 20 | 187168609978022860 |
| 21 | 1759888050471704664 |
| 22 | 16398685297890141180 |
| 23 | 151570887948878270348 |