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 | 24 |
| 5 | 120 |
| 6 | 420 |
| 7 | 1260 |
| 8 | 3472 |
| 9 | 9072 |
| 10 | 22860 |
| 11 | 56100 |
| 12 | 134904 |
| 13 | 319176 |
| 14 | 745108 |
| 15 | 1719900 |
| 16 | 3931680 |
| 17 | 8912352 |
| 18 | 20053404 |
| 19 | 44825940 |
| 20 | 99613960 |
| 21 | 220200120 |
| 22 | 484441188 |
| 23 | 1061157900 |
| 24 | 2315254704 |
| 25 | 5033163600 |
| 26 | 10905189100 |
| 27 | 23555209860 |
| 28 | 50734299672 |
| 29 | 108984793512 |