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 | -4 |
| 2 | 20 |
| 3 | -116 |
| 4 | 708 |
| 5 | -4452 |
| 6 | 28532 |
| 7 | -185300 |
| 8 | 1215268 |
| 9 | -8030404 |
| 10 | 53381844 |
| 11 | -356577588 |
| 12 | 2391430020 |
| 13 | -16092704292 |
| 14 | 108605848116 |
| 15 | -734783381652 |
| 16 | 4982063186916 |
| 17 | -33844621986180 |
| 18 | 230306722637204 |
| 19 | -1569571734301172 |
| 20 | 10711405584991300 |
| 21 | -73188920628617956 |
| 22 | 500643475619050740 |