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 | 3 |
| 1 | -4 |
| 2 | 12 |
| 3 | -40 |
| 4 | 140 |
| 5 | -504 |
| 6 | 1848 |
| 7 | -6864 |
| 8 | 25740 |
| 9 | -97240 |
| 10 | 369512 |
| 11 | -1410864 |
| 12 | 5408312 |
| 13 | -20801200 |
| 14 | 80233200 |
| 15 | -310235040 |
| 16 | 1202160780 |
| 17 | -4667212440 |
| 18 | 18150270600 |
| 19 | -70690527600 |
| 20 | 275693057640 |
| 21 | -1076515748880 |
| 22 | 4208197927440 |
| 23 | -16466861455200 |