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 | 9 |
| 2 | 50 |
| 3 | 220 |
| 4 | 840 |
| 5 | 2912 |
| 6 | 9408 |
| 7 | 28800 |
| 8 | 84480 |
| 9 | 239360 |
| 10 | 658944 |
| 11 | 1770496 |
| 12 | 4659200 |
| 13 | 12042240 |
| 14 | 30638080 |
| 15 | 76873728 |
| 16 | 190513152 |
| 17 | 466944000 |
| 18 | 1133117440 |
| 19 | 2724986880 |
| 20 | 6499598336 |
| 21 | 15386804224 |
| 22 | 36175872000 |
| 23 | 84515225600 |
| 24 | 196293427200 |
| 25 | 453437816832 |