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 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 68 |
| 5 | 224 |
| 6 | 672 |
| 7 | 1584 |
| 8 | 880 |
| 9 | -22880 |
| 10 | -215072 |
| 11 | -1414400 |
| 12 | -8012032 |
| 13 | -41344000 |
| 14 | -198120448 |
| 15 | -884348160 |
| 16 | -3640426752 |
| 17 | -13403384320 |
| 18 | -40424947200 |
| 19 | -65476561920 |
| 20 | 329862128640 |
| 21 | 4603911045120 |
| 22 | 35276325027840 |
| 23 | 221747978649600 |
| 24 | 1244854463643648 |